1. family and parenting
2. motherhood
3. pregnancy

review
Pregnancy loss and thrombophilia: the elusive link
Sarah A. Bennett,1 Catherine N. Bagot2 and Roopen Arya1
1
2
King’s Thrombosis Centre, Department of Haematological Medicine, King’s College Hospital NHS Foundation Trust, London and
Department of Haematology, Glasgow Royal Infirmary, Glasgow, UK
Summary
Recurrent pregnancy loss (RPL) affects 1% pregnancies and
is multi-factorial in origin. The role of the acquired thrombophilia antiphospholipid syndrome (APS) as a common
and potentially treatable cause of RPL is well established but
this is less so for inherited thrombophilia. In obstetric APS
the combination of aspirin and heparin has improved outcomes. By analogy, the use of low molecular weight heparin
(LMWH) has become commonplace in women with inherited thrombophilia and also those with unexplained miscarriage to help safeguard the pregnancy. This review will
examine the pathophysiological role of thrombophilia in
pregnancy loss, and the evidence for anticoagulant-based
intervention. The limited data supporting the use of heparin
for women with RPL and inherited thrombophilia suggests
adoption of a more cautious and judicious approach in this
setting.
Keywords: thrombophilia, miscarriage, fetal loss, heparin,
antiphospholipid syndrome.
Pregnancy is a prothrombotic state and a pathological exaggeration of this hypercoagulability has been increasingly
linked to pregnancy loss and placenta-mediated complications. Pregnancy loss is a very significant public health issue,
associated with maternal morbidity and mortality and psychological trauma. The term miscarriage is defined as the
spontaneous loss of a fetus before it reaches viability and
occurs in up to 15% of clinically recognized pregnancies
(Creagh et al, 1991; Warburton & Fraser, 1964). The World
Health Organization defines miscarriage as occurring prior to
20 weeks, however the Royal College of Obstetricians and
Gynaecologists (RCOG) include losses up to 24 weeks of gestation (Regan et al, 2011; Zegers-Hochschild et al, 2009).
Recurrent miscarriage refers to three or more consecutive
losses and occurs in 1% of couples trying to conceive, a
Correspondence: Dr Sarah Bennett, King’s Thrombosis Centre,
Department of Haematological Medicine, King’s College Hospital
NHS Foundation Trust, Denmark Hill, London SE5 9RS, UK.
E-mail: [email protected]
ª 2012 Blackwell Publishing Ltd
British Journal of Haematology, 2012, 157, 529–542
figure that has not changed over the last 22 years (Stirrat,
1990; Younis et al, 1997). If the working definition of recurrent pregnancy loss (RPL) is altered to two or more losses,
5% of couples would be affected, further magnifying the
scale of the problem (Rai et al, 1996). The probability of
miscarriage following three consecutive first trimester losses
increases with maternal age; those 30 years have a 25%
chance of subsequent pregnancy loss, rising to almost 50%
for those aged 40 years (Clifford et al, 1997). Several other
risk factors have been implicated in RPL but, despite extensive investigations, a significant proportion remain unexplained (Regan et al, 2011). The majority of pregnancy losses
occur in the first trimester and a significant number are associated with fetal cytogenetic abnormalities (Hatasaka, 1994).
The incidence of aneuploidy in embryos lost between 6 and
20 weeks’ gestation is reported at c. 35%, with 4% of fetal
losses after this time attributed to chromosomal abnormalities (Hassold & Hunt, 2001). For women with RPL this
figure may be as high as 60% (Stern et al, 1996). Detailed
analysis has revealed that 55% of embryonic trophoblasts
from women with primary RPL are chromosomally abnormal, compared to 35% of women with secondary RPL (i.e.
RPL following a previous successful pregnancy) (Coulam
et al, 1996). Importantly, the prognosis for a live birth in
subsequent pregnancies appears to be superior after miscarriage of an aneuploid rather than an euploid embryo (Carp
et al, 2001; Ogasawara et al, 2000; Stephenson et al, 2002).
This might suggest that there is an alternative cause for the
loss of euploid embryos, other than the anomalous chromosomal duplication and as such, abnormal euploidy may be a
significant confounder when evaluating treatments (Carp
et al, 2001; Coulam et al, 1996). Structural maternal abnormalities, such as congenital uterine anomalies and cervical
weakness, may also contribute to RPL, particularly in the second trimester, and the role of endocrine factors, infections
and immune dysfunction in the aetiology of RPL remains
contentious (Rai, 2008). Antiphospholipid syndrome (APS)
is an important treatable cause of RPL. Women with
untreated APS have a live birth rate of 10%, increasing to
42% with low dose aspirin and 71% using a combination of
aspirin and unfractionated heparin (Rai et al, 1997). As APS
is a prothrombotic state it has been conjectured that other
thrombophilic conditions might also be linked to RPL, hence
First published online 26 March 2012
doi:10.1111/j.1365-2141.2012.09112.x
Review
the increased interest in inherited thrombophilia as a potential cause. Given the experience in APS and driven in part by
the demand for some form of intervention by distressed couples, there has been a tendency for increasing and, sometimes, indiscriminate usage of anticoagulation in women
with unexplained pregnancy loss (which may include those
with inherited thrombophilias). In this review we examine
the evidence for the association between RPL and thrombophilia and the suggested interventions.
The association of inherited thrombophilia
with pregnancy loss
Inherited thrombophilia is common in the Caucasian population with a prevalence of up to 15% (Greer, 2003). Unsurprisingly, therefore, these abnormalities are commonly found
in women with RPL but this does not prove causation.
Interest in the role of inherited thrombophilia in this setting has grown since the publication in 1996 of a study
examining the risk of fetal loss in women with familial
thrombophilia enrolled in the European Prospective Cohort
on Thrombophilia (EPCOT) study (Preston et al, 1996). The
overall risk of pregnancy loss was increased in 571 women
with thrombophilia with an odds ratio (OR) of 1·35 [95%
confidence interval 1·01–1·82]. The OR was higher for stillbirth (3·6 [1·4–9·4]) than for miscarriage (1·27 [0·94–1·71])
and within this late fetal loss group (after 28 weeks of gestation) the OR was highest in women with combined defects
(14·3 [2·4–86·0]), followed by antithrombin deficiency (5·2
[1·5–18·1]), protein C deficiency (2·3 [0·6–8·3]), protein S
deficiency (3·3 [1·0–11·3]) and factor V Leiden (F5 R506Q)
(2·0 [0·5–7·7]). In the miscarriage groups (losses occurring at
or prior to 28 weeks of gestation) the corresponding ORs for
these inherited thrombophilias were 0·8 (0·3–2·6), 1·7 (1·0–
2·8), 1·4 (0·9–2·2), 1·2 (0·7–1·9) and 0·9 (0·5–1·5) respectively. With such wide confidence intervals, the majority of
which cross the boundary of 1·0, overall these data are
unconvincing for an association between inherited thrombophilia and pregnancy loss.
The TREATS (Thrombosis: Risk and Economic Assessment of Thrombophilia Screening) Study was a systematic
review of thrombophilia in pregnancy that included a total
of 79 studies; three randomized controlled trials, eight prospective cohorts and 68 retrospective studies (Robertson
et al, 2006). They examined the association between thrombophilia and early and late pregnancy loss separately. Twentyfive studies assessed thrombophilia in early losses (defined as
recurrent first or single second trimester); significant associations were observed with homozygous F5 R506Q (2·71 [1·32
–5·58]), heterozygous F5 R506Q (1·68 [1·09–2·58), F2 (prothrombin gene) mutation heterozygosity (2·49 [1·24–5·00]),
anticardiolipin antibodies (3·40 [1·33–8·68]), lupus anticoagulant (LA) (2·97 [1·03–8·56]), acquired activated protein C
resistance (4·04 [1·67–9·76]) and hyperhomocysteinaemia
(6·25 [1·37–28·42]). Analysis of the F5 R506Q data combined
530
both homozygotes and heterozygotes and found a higher risk
of pregnancy loss in the second (4·12 [1·93–8·81]) compared
to the first trimester (1·91 [1·01–3·61]). Similar to F5
R506Q, prothrombin mutation heterozygosity also increased
the risk of recurrent first trimester losses and non-recurrent
second trimester loss by OR 2·70 [1·37–5·35] and 8·6 [2·18–
33·95], respectively, with an association being most convincing for the latter. Fifteen studies related to late pregnancy
loss (defined as the third trimester) and showed an increased
risk in F5 R506Q heterozygotes (2·06 [1·10–3·86]), F2 mutation heterozygotes (2·66 [1·28–5·53]), protein S deficiency
(20·09 [3·7–109·15]) and anticardiolipin antibodies (3·30
[1·62–6·70]). While these pooled data are more suggestive of
an association, the wide confidence intervals, with the lower
boundary frequently close to one, and the heterogeneity of
the data, particularly pertaining to F5 R506Q and recurrent
first trimester losses (v2 = 23·66, df = 7, P = 0·001), again
signify the need for caution in interpretation.
A modest association was evident in another meta-analysis, which included a total of 31 studies (of which only two
were prospective cohorts) and again examined associations
according to the timing of the pregnancy losses (Rey et al,
2003). F5 R506Q was associated with early RPL (OR 2·01
[1·13–3·58]), late RPL (7·83 [2·83–21·67]) and late nonrecurrent fetal loss (3·26 [1·82–5·83]); F2 mutation with
early RPL (2·56 [1·04–6·29]) and late non-recurrent loss
(2·3 [1·09–4·87]); protein S deficiency was associated with
late non-recurrent fetal loss (7·39 [1·28–42·63]); protein C
and antithrombin deficiency were not significantly associated with any type of pregnancy loss. Due to the lower
prevalence of women with natural anticoagulant deficiencies
(antithrombin, protein C and protein S) there are far fewer
studies investigating their associations with adverse obstetric
outcomes and data thus far is based on low patient numbers. Without statements to the contrary, it is possible that
some women in these studies received antenatal venous
thromboembolism (VTE) prophylaxis. In turn, if the mechanism of pregnancy loss in these patients is due to thrombosis in uteroplacental vessels it is possible that the
prophylactic therapy may have contributed to the success
of the pregnancy and therefore any association may be
missed.
Thrombophilia and the pathophysiology of
pregnancy loss
Antiphospholipid syndrome
Pregnancy loss in APS has traditionally been ascribed to
uteroplacental thrombosis and was first considered after the
finding of massive placental infarction in a lupus anticoagulant (LA) positive woman who experienced an intrauterine
death (De Wolf et al, 1982). Similar findings from women
with antiphospholipid (aPL) antibodies and pregnancy loss
supported this theory (Out et al, 1991). Recently there has
ª 2012 Blackwell Publishing Ltd
British Journal of Haematology, 2012, 157, 529–542
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been more interest in the role of the trophoblast and endometrial invasion and implantation, with focus on an underlying immunomodulatory, rather than purely thrombotic
process. Histopathological examination of products of conception in women with primary APS and pregnancy losses
between 7 and 10 weeks’ gestation attributed these losses to
abnormal endovascular trophoblast invasion in decidual vessels rather than excessive intervillous thrombosis (Sebire
et al, 2002). Complement activation has previously been
reported as causative in aPL antibody-induced fetal injury,
with suggestions that heparin was beneficial due to anti-complement rather than anticoagulatory effects (Girardi et al,
2004). Murine experiments supported this theory as both unfractionated heparin (UFH) and the low molecular weight
heparin (LMWH) enoxaparin (even at sub-therapeutic dosage) demonstrated an inhibitory effect on complement activation and protected mice from aPL antibody-induced
pregnancy complications; neither fondaparinux (a specific
inhibitor of clotting factor Xa) nor hirudin (a direct thrombin inhibitor) had either effect (Girardi et al, 2004). A third
proposed mechanism of pregnancy loss in women with APS
concerns annexin V. Previously known as placental anticoagulant protein 1, annexin V is produced by villous trophoblasts and has potent anticoagulant activity due to a high
affinity for anionic phospholipids (Rand et al, 1997). Clustering of annexin V on phospholipid surfaces results in
displacement of clotting factor Va, precluding formation of
procoagulant complexes (Andree et al, 1992). Thus, removal
of annexin V from trophoblast membranes (for example by
anti-annexin V or aPL antibodies) induces a procoagulant
surface; markedly reduced levels on placental villi have been
demonstrated in women with APS (Krikun et al, 1994; Rand
et al, 1994).
Another mechanism is suggested by murine studies,
which demonstrated that passive transfer of a human
monoclonal antiphospholipid antibody, CIC15, isolated
from a patient with primary APS and recurrent early pregnancy losses induced fetal resorption (Lieby et al, 2004).
Histological analysis revealed signs of decidual arterial
thrombosis, but there was no evidence of inflammatory cell
infiltration in the decidual or fetal tissue. CIC15 was unable
to disrupt the annexin V shield (unlike other aPL antibodies), suggesting that pregnancy loss was neither due to displacement of annexin V from trophoblast surfaces nor
inflammation. Although the precise pathogenicity remains
to be identified, in vitro experiments support the idea that
pregnancy loss in this setting was probably related to the
procoagulant activity of CIC15 (Poindron et al, 2011). Analogous to the earlier heparin experiments (Girardi et al,
2004), this more recent work demonstrated that LMWH
(tinzaparin at a therapeutic dose) completely protected mice
from fetal injury induced by CIC15. Both fondaparinux and
hirudin were also protective, suggesting that CIC15-mediated fetal injury is largely a consequence of a prothrombotic
effect.
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British Journal of Haematology, 2012, 157, 529–542
Inherited thrombophilia
The underlying aetiology of pregnancy failure is likely to
depend on the timing of loss and whether it occurs during the
pre-embryonic, embryonic or fetal stage of development. The
pre-embryonic stage commences with zygote formation and
endometrial implantation and continues until week 6 of gestation. Fetal aneuploidy accounts for c. 20% losses during this
pre-embryonic stage (Hassold & Hunt, 2001). However, it is
following implantation when the foundations are laid for connections between the developing trophoblast and maternal
blood. Very early work on morphological specimens of human
ova demonstrated that even as early as 2 d post-implantation
lacunar spaces have developed in the trophoblast, which, over
the next few days, form communications with the maternal
endometrium and blood supply to enable further growth and
development (Hertig et al, 1956). It is therefore possible that
inherited thrombophilias could play a role at this very early
stage by disrupting the development of this intricate blood
supply and confer a disadvantage for implantation. Yet there
is evidence contrary to this to suggest that heterozygosity for
F5 R506Q may in fact aid implantation: A study of 102
mother-child pairs following in vitro fertilization (IVF) treatment, demonstrated that in 90% of F5 R506Q positive pairs,
the first embryo transfer was successful (defined as successful
implantation of the embryo) compared with 49% in F5
R506Q negative pairs (P = 0·018). Furthermore, the median
number of successful transfers was significantly higher in pairs
who were positive for the mutation (P = 0·02) (Gopel et al,
2001). Although these findings have not been replicated on a
larger scale, results from the Multiple Environmental and
Genetic Assessment (MEGA) study demonstrated that while
carriage of F5 R506Q had no association with fecundity or
rates of miscarriage, when miscarriage did occur it was less
likely to be during the first trimester in women who carried
the mutation, compared to those who did not (van Dunne
et al, 2005). This may be suggestive of a protective influence
over implantation or early embryonic development in F5
R506Q carriers (van Dunne et al, 2005). Furthermore, data
from the Leiden 85-Plus study demonstrated that fecundity
(defined as the time from marriage to firstborn child) was
unrelated to maternal F5 R506Q status. In spite of these data,
in the absence of evidence regarding pregnancies that ended
in miscarriage or stillbirth, the proposed protective effect of
this thrombophilia in early pregnancy at least, still cannot be
examined (van Dunne et al, 2006).
The embryonic period follows at week 6 when the embryo
derives its blood supply from the yolk sac, a role which is
gradually taken over by the placenta between weeks 8 and
10, becoming exclusive at the beginning of week 10 (Makikallio et al, 1999). It is thought that the maternal blood supply does not convincingly contribute to fetal development
until the end of this stage but, as detailed above, there is a
potential role for prothrombotic factors to influence integrity
of blood flow prior to 6 weeks of gestation. The fetal stage
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of development commences at the beginning of the 10th
week of gestation and continues until delivery. If thrombophilias cause pregnancy loss as a result of thrombosis in
uteroplacental vessels the fetal stage would present a vulnerable period for these events.
Research has also focused on the protein C pathway:
Protein C is activated by the thrombin-thrombomodulin
complex and behaves as an anticoagulant by deactivating
clotting factors Va and VIIIa in the presence of a co-factor,
protein S. Transgenic mouse models have demonstrated that
the protein C system forms an essential component in the
maintenance of pregnancy beyond trophoblast invasion, not
as a result of its antithrombotic properties, but due to its
enhancement of trophoblast viability and growth (Isermann
et al, 2003; Lay et al, 2005). Thrombomodulin-deficient mice
showed very early developmental failure and did not survive
beyond 8·5 d post coitum, moreover they were completely
resorbed in the following 24 h (Isermann et al, 2003).
Embryonic death was thought to have been caused by tissue
factor-initiated activation of the clotting cascade at the
feto-maternal interface, mediated by both fibrin and protease-activated receptors PAR-2 and PAR-4. Notably, high
molecular weight heparin and warfarin were both shown to
delay resorption of thrombomodulin-deficient mice, although
they were not able to overcome the associated growth defects
(Isermann et al, 2003). The authors proposed that thrombin
may play a key role in cell signalling and contribute to
trophoblastic apoptosis and impairment of trophoblast invasion. This study is one of the few to provide pathophysiological evidence for a link, albeit in the embryo, between
inherited thrombophilia and RPL. There is otherwise very
little supportive experimental or histological data, with minimal evidence for the placental thrombosis that is frequently
implicated in these cases.
Paternal and fetal thrombophilias
Given that the placenta has a dual blood supply, derived
from mother and fetus, it has been suggested that paternal or
fetal thrombophilia status may be implicated in pregnancy
loss (Dizon-Townson et al, 1997; Jivraj et al, 2006). The
hypothesis for paternal thrombophilia involvement has not
been supported by the findings from two studies, which
reported no effect of paternal thrombophilia on the frequency of early or late losses (Gris et al, 1999; Preston et al,
1996). Furthermore another recent study has shown that the
prevalence of F5 R506Q and F2 mutations was no greater in
male partners of recurrent miscarriage patients compared to
controls (Toth et al, 2008).
Evidence from knock-out mice embryos has shown that
the fetal genotype may exert an important prothrombotic
effect on placental trophoblasts (Sood et al, 2007). The
authors went on to hypothesize a synergistic effect of maternal and fetal prothrombotic mutations on pregnancy loss.
Convincing evidence for this in humans does not exist. A
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large population-based study screened 85 304 newborn
infants for both F5 R506Q and F2 mutations and identified
the expected number of F5 R506Q homozygotes or double
heterozygotes, suggesting that fetal thrombophilia does not
increase the risk of pregnancy loss (Hundsdoerfer et al,
2003). Also, heparin does not cross the placenta; thus, if
thrombophilic factors in the fetal circulation do influence
pregnancy outcome they would be unlikely to be modified
by this therapy.
Thrombophilia testing in women with
unexplained recurrent pregnancy loss
The frontline investigations for RPL include cytogenetic analysis on products of conception (with parental karyotyping
required in some cases), pelvic ultrasound scanning and testing
for APS (LA and anticardiolipin antibodies) (Jauniaux et al,
2006). If these tests are unrewarding, testing for the inherited
thrombophilias is often considered, based on the pattern of
losses and clinical factors such as placental histology.
Antiphospholipid antibodies
The requirements for a diagnosis of APS are well established,
with a panel of clinical criteria and reproducibly positive laboratory tests (summarized in Table I). Persistently positive
LA or aPL antibodies [anti-cardiolipin (aCL) IgG or IgM
antibodies] are found in c. 15% of women with RPL (three
or more consecutive losses) with LA being the most commonly detected (Rai et al, 1995). In contrast, isolated aPL
antibody positivity has been demonstrated in up to 3% of
unselected women of childbearing age and was not predictive
of poor pregnancy outcome (Creagh & Greaves, 1991). The
updated Sapporo classification criteria for APS include
Table I. Diagnosis of antiphospholipid syndrome* (requires one
clinical and one laboratory criterion).
Clinical criteria
Vascular thrombosis – arterial or venous (excluding superficial vein
thrombosis)
Pregnancy morbidity
Unexplained pregnancy loss of a morphologically normal fetus
10 weeks’ gestation
Premature birth (<34 weeks’ gestation) due to (pre-)eclampsia or
other cause of placental insufficiency
3 unexplained consecutive pregnancy losses <10 weeks’
gestation
Laboratory criteria (present on at least two occasions, 12 weeks
apart)
LA
aCL antibody (IgG/IgM)
Anti-b2 GP1 antibody (IgG/IgM)
LA, lupus anticoagulant; aCL, anticardiolipin; Anti-b2 GP1,
anti-beta2 glycoprotein-1.
*Adapted from Miyakis et al (2006).
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British Journal of Haematology, 2012, 157, 529–542
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positivity for anti-b2 glycoprotein-1 (anti-b2 GP1) IgG and
IgM antibodies (Miyakis et al, 2006). This recommendation
is predominantly based on an association with VTE (Lee
et al, 2003). The recommendation for testing for anti-b2 GP1
antibodies in the adverse obstetric outcome group is based
on two studies. The first is a prospective study of 510 lowrisk pregnant women tested between 15 and 18 weeks’ gestation; 20 women (3·9%) tested positive for anti-b2 GP1 on
one occasion, with only two women developing complications of pre-eclampsia/eclampsia (Faden et al, 1997). In the
second study, anti-b2 GP1 IgA antibodies (together with
higher levels of autoantibodies) were more commonly found
in women with unexplained recurrent miscarriages where LA
and aCL IgG antibodies were negative; however, whether
they were directly pathogenic, a sequelae of the pregnancy
loss itself or associated with an alternative underlying autoimmune disorder was uncertain (Lee et al, 2001). Results
from two other studies demonstrated no significant increase
in prevalence of anti-b2 GP1 IgG antibodies in women with
RPL, when defined as three or more consecutive pregnancy
losses (Ailus et al, 1996; Arnold et al, 2001). The significance
of anti-b2 GP1 antibody testing in the RPL population
requires further clarification (Miyakis et al, 2006; Nash et al,
2004). There are additional assays which detect other phospholipid binding proteins and it is possible that in the future
these may be important in the evaluation of APS; examples
are antibodies to phosphatidylserine, prothrombin, phosphatidylethanolamine, phophatidylinositol, phosphatidylglycerol,
and those against the phosphatidylserine-prothrombin complex (Franklin & Kutteh, 2002; Miyakis et al, 2006).
Acquired activated protein C resistance
Activated protein C resistance (APCR) may occur in the
absence of mutations in F5, a phenomenon known as
acquired APCR (Clark & Walker, 2001). The original test
uses an activated partial thromboplastin time (aPTT)-based
assay and provides a ratio of the aPTT in the presence and
absence of added APC; a lower ratio indicating greater resistance (Dahlback et al, 1993). This may represent a prothrombotic tendency as the degree of resistance has been
related to thrombin generation and risk of VTE (Clark et al,
1999; de Visser et al, 1999). Of 280 consecutive women with
RPL (three consecutive losses prior to 24 weeks’ gestation),
51 were found to have acquired APCR in a regional UK miscarriage clinic (Dawood et al, 2003). Compared to a control
group of 102 women from the initial cohort, matched for
age and number of previous pregnancy losses, the overall retrospective fetal loss rate was significantly increased at 75%
vs. 39% of all pregnancies (OR 1·91[1·42–2·55]). In a large
prospective study of 2480 unselected pregnant women, those
with acquired APCR demonstrated an overall increased association with second trimester losses, (OR 2·8 [1·3–6·1])
(Lindqvist et al, 2006). The statistical significance was lost
when considering outcomes of the current pregnancy only.
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British Journal of Haematology, 2012, 157, 529–542
In favour of an association with pregnancy loss is a study
of 1111 Caucasian women in whom acquired APCR was
demonstrated in 8·8% of women with RPL (three consecutive losses prior to 12 weeks’ gestation) and 8·7% of women
with a single loss after 12 weeks’ gestation; both significantly
more common than in the control population of 150 women
(3·3%), P = 0·02 and P = 0·04 respectively (Rai et al, 2001).
However the GOAL (Glasgow Outcome, APCR and Lipid)
study assessed 1671 pregnant, non-F5 R506Q subjects and
found no significant relationship between the APCR ratio at
any gestation and fetal loss (Clark et al, 2001).
F5 R506Q (factor V Leiden) and F2 G20210A mutations
The worldwide prevalence of the most common thrombophilic mutations, F5 R506Q and F2 mutations, varies widely. In
UK Caucasian and healthy European populations these mutations have a prevalence of around 8·8% and 1·7–3% respectively (Rees et al, 1995; Rosendaal et al, 1998). F5 R506Q is
absent in indigenous populations from Africa, Southeast Asia
and Australasia but, by contrast, has a prevalence of up to
15% and 13% in Greeks and Middle Eastern ethnic groups,
respectively (Awidi et al, 1999; Irani-Hakime et al, 2000).
Similarly F2 G20210A prevalence varies; 6·7% in Ashkenazi
(European) Jews; limited presence in those of non-European
origin; absent in the UK black, Indian and Chinese populations and Ethiopian Jews (Patel et al, 2003; Vora et al, 2008;
Wang et al, 2006; Zivelin et al, 1998). As one might expect,
ethnicity appears to be a confounding factor when examining
an association between thrombophilia and pregnancy loss. A
meta-analysis considered this issue with regard to F5 R506Q
and found a weaker association for non-Israeli compared to
Israeli women (OR 1·83 [1·47–2·29], OR 3·45 [2·47–4·82]
respectively) (Kist et al, 2008). Concurring with this was the
degree of distinction seen between F5 R506Q and RPL when
restricting analysis to studies recruiting only white women
compared to those with mixed populations (OR 1·5 [1·1–
2·2], OR 3·4 [2·2–5·1] respectively) (Kovalevsky et al, 2004).
Therefore, when testing for these two inherited thrombophilias, the ethnic origin of the patient needs to be considered.
Natural anticoagulant deficiencies
Deficiencies of the natural anticoagulants, antithrombin
(AT), protein C (PC) and protein S (PS) are usually detected
by chromogenic and enzyme-linked immunosorbent assays,
which are currently more practical than DNA analysis
because deficiencies of the natural anticoagulants can be due
to any of more than 100 mutations in the respective genes
(SERPINC1, PROC and PROS1). Their prevalence in healthy
European populations is low; 0·02% for AT, 0·2–0·4% PC
and 0·03–0·13% for PS deficiency (Franco & Reitsma, 2001;
Tait et al, 1994). In non-European populations there is less
data, although Japanese blood donors have been shown to
have a prevalence of 0·15% for AT, 0·13% for PC and 1·12%
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for PS deficiency (Sakata et al, 2004a,b). PC and PS levels
were found to be significantly lower in black subjects than
the reference range derived from a white population, with a
trend towards lower antithrombin levels (Jerrard-Dunne
et al, 2003). There are therefore likely to be different thresholds for pathological levels of natural anticoagulants in different populations, so normal ranges should be derived from
healthy individuals within a comparable ethnic group.
Plasma levels of AT and PC are generally unchanged during
pregnancy although both may increase post-partum (Clark
et al, 1998; Hellgren & Blomback, 1981; Szecsi et al, 2010).
Protein S exists in plasma both free (40%) and bound to the
complement C4b binding protein (60%). Protein S levels
therefore fluctuate more widely than the other natural anticoagulants, and it is the free portion that is active and complexes as a cofactor with activated PC. Therefore conditions
that increase complement, including pregnancy, will reduce
protein S activity (Clark et al, 1998; Szecsi et al, 2010). The
hypercoagulable changes of pregnancy have largely resolved
by 6 weeks post-partum, consequently testing for deficiencies
in the natural anticoagulants should in usual circumstances be
deferred until at least after this time period (Maybury et al,
2008; Saha et al, 2009). If screening for protein S is necessary
during pregnancy then an adjusted reference range may be
appropriate (Lockwood & Wendel, 2011). Based on free protein S antigen levels in 102 women tested during the second
and third trimesters, lower limits of normality were suggested
at 29% and 23% respectively (Paidas et al, 2005).
Hyperhomocysteinaemia
Hyperhomocysteinaemia has been linked variably to RPL
(Nelen et al, 2000; Quere et al, 1998). Individuals who are
homozygous for methylene tetrahydrofolate reductase gene
(MTHFR) mutations can have normal homocysteine levels
making the usefulness of gene testing questionable in this
population. The value of testing homocysteine levels per se in
the investigation of pregnancy loss is also debatable. It is
possible that folic acid taken in pregnancy could reduce
homocysteine levels and mask any potential association with
RPL. Not only is there incomplete reported data on the use
of vitamin supplements in studies, but the timing and methodology of testing (e.g. fasting state, use of methionine load)
also differs between them. There does not appear to be an
independent association between homozygous MTHFR mutation and RPL and, due to the reasons given above, the role
of hyperhomocysteinaemia in pregnancy loss is difficult to
examine (Holmes et al, 1999; Rey et al, 2003).
Global coagulation assays
The role of global coagulation testing in defining thrombophilia in women with RPL has yet to be determined. Outside
of APS, the overall weak association between thrombophilia
and pregnancy loss may either reflect the absence of an
534
underlying thrombotic aetiology, or demonstrate the insensitivity of currently available thrombophilia tests to detect a
thrombotic risk. If a baseline hypercoagulable state or an
exaggerated prothrombotic response in pregnancy are risk
factors for pregnancy loss, it may be worthwhile to assess the
overall ability of the blood to clot, rather than examine individual coagulation parameters. Thromboelastography (TEG),
which measures fibrin clot strength and stability in whole
blood, may be a useful assay to detect hypercoagulable states.
Previous studies using TEG have demonstrated hypercoagulable parameters in normal pregnancy compared to nonpregnant women, with the greatest effect seen during labour
(Gorton et al, 2000; Steer & Krantz, 1993). Return of parameters to baseline levels have been demonstrated at 4 weeks
postpartum (Maybury et al, 2008). There is evidence to suggest that some women with recurrent miscarriages are
prothrombotic outside of pregnancy. Four hundred and
ninety-four women with a history of RPL (three consecutive
miscarriages prior to 12 weeks’ gestation) were prospectively
shown to have a significantly higher MA (maximum amplitude, a measure of maximum clot strength) than controls
when using TEG, and moreover, these women also demonstrated reduced clot lysis when measured at 30 min (LY30, a
measure of clot stability), both P = 0·01 (Rai et al, 2003).
Another group assessed 588 unselected pregnant women at a
mean gestational age of 13·6 weeks (range 6–38 weeks) and
demonstrated that the only outcome to correlate with TEG
parameters was mid-trimester loss (12–23 weeks) (Miall et al,
2005). Although there were only seven such women, they all
demonstrated enhanced coagulability compared to all the
other women, with a significantly lower mean R time (time
to initial fibrin formation) P < 0·03 (Miall et al, 2005).
Calibrated automated thrombography also assays global
coagulation. With the aid of a fluorometer it measures the
amount of thrombin generated when tissue factor is used to
initiate coagulation in plasma in the presence of exogenous
phospholipid. An additional feature of this test is that
thrombomodulin can be added to assess the activated protein
C pathway. One group have demonstrated that, in the presence of thrombomodulin, significantly enhanced thrombin
generation was seen in women with a history of RPL (two or
more consecutive losses prior to 21 weeks’ gestation) compared to controls, P = 0·001 (de Saint Martin et al, 2011).
This result could indicate a relative thrombomodulin resistance in subjects alluding to the importance of the protein
C pathway in protecting pregnancy.
Anticoagulant and antiplatelet interventions to
reduce recurrent pregnancy loss
With supportive care alone the overall chance of a successful
pregnancy can be as high as 70–75% following recurrent
miscarriage (Brigham et al, 1999; Clifford et al, 1997;
Stray-Pedersen & Stray-Pedersen, 1984). An even higher
success rate than this would be expected when considering
ª 2012 Blackwell Publishing Ltd
British Journal of Haematology, 2012, 157, 529–542
Review
the efficacy of future treatment and this may be difficult to
establish, particularly as placebo controlled trials are in short
supply.
Aspirin
Aspirin is commonly prescribed to women at high risk of
obstetric complications (including pregnancy loss, pre-eclampsia/eclampsia, intrauterine growth restriction and placental
abruption) as well as to those undergoing assisted conception.
The hypothesis underlying the benefit afforded by aspirin in
obstetric complications, including RPL, is the effect on trophoblast implantation and uteroplacental vessel integrity.
The basis for use in IVF stems from the attribution of
uterine vessel hypoperfusion as a cause of embryonic implantation failure (Goswamy et al, 1988). The anti-thrombotic
properties of aspirin may act to improve blood flow here via
inhibition of thromboxane A2, which is required for platelet
aggregation. With the additional stimulation of IL-3, an
essential factor for implantation and placental growth, by
aspirin, a more favourable environment for embryonic
implantation may be created (Fishman et al, 1993). It is also
suggested that aspirin may increase endometrial thickness,
and in turn improve implantation rates when intracytoplasmic sperm injection treatment is used. In spite of these
plausible mechanisms, there is a lack of data to recommend
aspirin in the IVF setting, thus its use is not evidence based.
A recently updated Cochrane review confirmed this, identifying the need for adequately powered trials (Siristatidis et al,
2011).
There is some evidence to suggest that aspirin can reduce
pregnancy loss in women with APS, from studies demonstrating improved live birth rates over placebo (Kutteh, 1996;
Rai et al, 1997). However, there is also evidence to suggest
that there may be no additional benefit. A pilot doubleblinded randomized controlled trial (RCT) reported live
birth rates of 80% and 85% in aspirin and placebo treatment
groups, respectively, in women with APS, a difference which
was not statistically significant (Pattison et al, 2000). Pending
adequately powered RCTs the true ability of aspirin to
prevent pregnancy loss remains to be determined.
Anticoagulation in antiphospholipid syndrome
In light of the perceived association between placental vessel
thrombosis and pregnancy loss in women with APS, numerous trials have been performed to assess the efficacy of prophylactic anticoagulation in these cases, although very few
have been placebo controlled (Table II). UFH has traditionally been the anticoagulant of choice during pregnancy
Table II. Studies of anticoagulant and antiplatelet-based treatment in women with antiphospholipid syndrome.
Authors
Subject inclusion criteria
Exclusions
Interventions and live birth rate (%)
Kutteh (1996)
3 consecutive losses
Positive aPL antibodies on two occasions (aCL
or antiphosphatidylserine antibodies)
SLE
LA positivity
Prior VTE
Rai et al (1997)
3 consecutive losses
LA or aCL positivity on two or more
occasions, at least 8 weeks apart
SLE
Prior VTE
Farquharson
et al (2002)
3 consecutive losses or 2 losses occurring
after 10 weeks’ gestation
LA or aCL positivity on two occasions at least
6 weeks apart
RPL
Broad inclusion criteria (positivity for aPL
antibody or ANA or inherited
thrombophilias)
Persistent positivity for LA or aCL antibodies
3 losses <10 weeks or 1 loss >10 weeks
SLE
Prior VTE
Aspirin 81 mg (n = 25) 44%
vs.
Aspirin 81 mg + UFH 5000 iu twice daily
(n = 25) 80%
Aspirin 75 mg (n = 45) 42%
vs.
Aspirin 75 mg + UFH 5000 iu twice daily
(n = 45) 71%
Aspirin 75 mg (n = 47) 72%
vs.
Aspirin 75 mg + LMWH (ns) 5000 iu once
daily (n = 51) 78%
Aspirin 81 mg (n = 43) 79%
vs.
Aspirin 81 mg + dalteparin 5000 iu once daily
(n = 45) 77·8%
Aspirin 81 mg + dalteparin (n = 14) 69%
vs.
Aspirin 81 mg + UFH (n = 14) 31% (heparin
dose variable in trimesters)
Aspirin 81 mg + enoxaparin 40 mg (n = 25)
84%
vs.
Aspirin 81 mg + UFH 5000 iu twice daily
(n = 25) 80%
Laskin et al
(2009)
HepASA trial
Stephenson
et al (2004)
Noble et al
(2005)
3 consecutive losses <20 weeks
Positive LA or aPL antibodies on at least two
occasions, at least 6 weeks apart
SLE
Prior VTE
Inherited
thrombophilias
Prior heparin use
–
SLE, systemic lupus erythematosus; ANA, antinuclear antibodies; VTE, venous thromboembolism; UFH, unfractionated heparin; LMWH, low
molecular weight heparin; ns, not specified; aCL, anticardiolipin; LA, lupus anticoagulant; aPL, antiphospholipid; RPL, recurrent pregnancy loss.
ª 2012 Blackwell Publishing Ltd
British Journal of Haematology, 2012, 157, 529–542
535
Review
(Sanson et al, 1999). More recent studies have chosen to
assess LMWHs due to their advantages over UFH, which
include easier administration (once daily) and lower incidences of both osteoporosis and heparin induced thrombocytopenia (Greer & Nelson-Piercy, 2005).
A non-randomized prospective study of women with a history of three consecutive losses and positive aPL antibodies,
compared low dose aspirin alone (n = 25) and in combination with prophylactic dose UFH (n = 25) and demonstrated
live birth rates of 44% and 80% respectively (Kutteh, 1996).
The additional benefit of UFH was confirmed in a subsequent
randomized, non-blinded trial which examined a similar
cohort of women who fulfilled both the clinical and laboratory criteria for APS, and found the live birth rate increased
from 42% to 71% with the combination treatment (n = 45)
compared to aspirin alone (n = 45) (Rai et al, 1997). Based
on these two trials, a Cochrane review concluded that the
addition of UFH to aspirin may reduce pregnancy loss by
54% RR 0·46 (0·29–0·71) (Empson et al, 2005).
Similar results have not been shown with aspirin in combination with LMWH; two trials demonstrated no additional
benefit (Farquharson et al, 2002; Laskin et al, 2009). However, there have been reservations about the validity of the
results from the 2002 study as randomization occurred up to
a relatively late gestation (12 weeks), women with low aCL
antibody titres were included and there was a high cross-over
rate with 25% not receiving allocated treatment (Kutteh,
2002; Rai & Regan, 2002; Rodger & Paidas, 2007). Furthermore, in the later trial only 48% of the 88 women in the
study were positive for aPL antibodies (Laskin et al, 2009).
There is very little data that adequately assesses the efficacy of UFH compared to LMWH. Two pilot studies have
compared prophylactic doses of each in combination with
aspirin. The first study concerned 28 women (with either
three prior losses before 10 weeks’ gestation or one loss
thereafter) in whom prophylactic dose dalteparin was compared to UFH (increasing doses of each as pregnancy progressed) and resulted in live birth rates of 69% vs. 31%
respectively (Stephenson et al, 2004). The authors suggested
that LMWH may be an effective alternative to UFH although
the live birth rate with UFH was disproportionately low,
putting into question the validity of the results. The second
study, which recruited women with three consecutive losses
prior to 20 gestational weeks, compared enoxaparin (40 mg
daily) with UFH both in combination with low dose aspirin
(n = 25 in both groups) and reported very similar live birth
rates of 84% and 80% respectively (Noble et al, 2005).
Both the British and American guidelines propose combination treatment (aspirin with UFH or LMWH) for women
with RPL and aPL antibodies not withstanding the limited
data (Bates et al, 2012; Keeling et al, 2012; Regan et al,
2011). Doubt remains regarding the true benefit of this treatment (Branch, 2011; Empson et al, 2005; Jauniaux et al,
2006; Laskin et al, 2009; Pierangeli et al, 2011). Furthermore,
the optimal timing of initiation and unpredictable pharma536
cokinetic profile of LMWH in pregnancy are important factors that have not been adequately investigated (Patel et al,
2011). In the studies described above, the timing of heparin
initiation was also variable and in some cases was introduced
only after fetal heart activity was confirmed. There is evidence to suggest that heparin may prove beneficial if started
before this stage in embryonic development by having an
advantageous influence on implantation (Nelson & Greer,
2008). Unfortunately, the period of time from attempting to
conceive to successful conception is highly variable and prolonged use of heparin would not be appropriate. Therefore
further research is required to explore this issue before preimplantation heparin intervention is promoted as beneficial
to pregnancy outcomes.
Anticoagulation in inherited thrombophilias
Controversy remains regarding the link between inherited
thrombophilia and RPL and it is therefore unsurprising that
there is intense debate as to whether the use of anticoagulation is beneficial in improving pregnancy outcomes for this
group of women. Over the years, various groups have demonstrated an improvement in live birth rates with the use of
anticoagulants (Table III). However the design of these studies and the low numbers of patients recruited mean that the
applicability of the results is extremely limited. There is a
danger that non-discriminatory thrombophilia testing is
encouraged by these studies and that ‘positive’ results
encourage interventions that are not evidence based.
A retrospective study of 24 women with an inherited
thrombophilia (F5 R506Q or F2 mutations, or AT, PC or PS
deficiency) found that those who received UFH (5000 units
twice daily commenced at positive pregnancy testing) had a
more favourable outcome compared to those without treatment; live birth rates of 100% and 59% respectively (Ogueh
et al, 2001). Interestingly, only six women had a history of
RPL and there was an obstetric complication rate of 35% in
each arm; the true benefit of UFH here is thus uncertain.
Subsequently the efficacy of LMWH has been assessed in
women with an inherited thrombophilia (as defined above)
who had experienced at least three consecutive losses in the
first or second trimesters. Those treated with enoxaparin
40 mg daily (n = 37) were compared to similar women who
did not receive LMWH (n = 48) and were found to have a
superior live birth rate of 70% vs. 44%, respectively (OR
3·03 [1·12–8·36]) (Carp et al, 2003). Heparin was started
at positive pregnancy testing, but the initiation was nonrandomized and fetal karyotyping on pregnancies that were
lost was incomplete.
A single centre study recruited women with either heterozygosity for F5 R506Q, F2 mutation or protein S deficiency
who had experienced one pregnancy loss after 10 weeks’ gestation, and compared low dose aspirin (n = 80) with 40 mg
enoxaparin daily (n = 80) commenced at the 8th week of
amenorrhoea after a positive pregnancy test; the latter
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British Journal of Haematology, 2012, 157, 529–542
Terminated or ectopic pregnancies
APS (LA or ACL antibodies)
Prior VTE
Known causes of pregnancy loss
APS (LA or ACL antibodies)
Prior VTE
Known causes of pregnancy loss
F5 R506Q/F2 mutation or PS deficiency
1 pregnancy loss >10 weeks
F5 R506Q/F2 mutation
Broad RPL criteria ( 3 in 1st trimester/ 2
in 2nd trimester/1 loss in 3rd trimester)
Women with AT/PC/PS deficiency taken from
a family cohort study who became pregnant
within the study period
RPL ( 2 losses 20 weeks’ gestation)
RPL ( 2 consecutive losses 24 weeks)
Gris et al
(2004)
Brenner et al
(2005)
LIVE-ENOX
Folkeringa
et al (2007)
Kaandorp
et al (2010)
ALIFE
Clark et al
(2010)
SPIN
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British Journal of Haematology, 2012, 157, 529–542
aPL antibodies
Any losses <10 weeks’ gestation
Prior VTE
Known causes of pregnancy loss
Prior VTE
APS (LA or aCL antibodies)
Prior VTE
Known causes of pregnancy loss
UFH 100%
No treatment 59%
UFH 5000 iu twice daily (pregnancy = 17) started
at positive pregnancy testing
vs.
No treatment (pregnancy n = 22)
Enoxaparin 40 mg (n = 37) started when
pregnancy recognized
vs.
No treatment (n = 48)
Aspirin 100 mg (n = 80)
vs.
Enoxaparin 40 mg (n = 80) started at 8 weeks of
amenorrhoea
Enoxaparin 40 mg daily (n = 89)
vs.
Enoxaparin 40 mg twice daily (n = 91) started
between 5–10 weeks’ gestation
UFH or LMWH or vitamin K antagonist at VTE
treatment doses started at pregnancy diagnosis
(n = 45 pregnancies)
vs.
No treatment (n = 19 pregnancies)
Aspirin 80 mg + nadroparin 2850 iu (n = 97)
vs.
Aspirin 80 mg alone (n = 99)
vs.
Placebo (n = 103) started at viable pregnancy
confirmed by ultrasound from 6 weeks’ gestation
Aspirin 75 mg + enoxaparin 40 mg (n = 143)
started after positive pregnancy testing
vs.
Placebo (n = 140)
Aspirin + LMWH 78%
Placebo 79%
Aspirin + LMWH 69·1%
Aspirin alone 61·6%
Placebo 67%
Treatment 98%
No treatment 42%
LMWH 40 mg 84·3%
LMWH 80 mg 78·3%
Aspirin 29%
LMWH 86%
LMWH 70·2%
No treatment 43·8%
Live birth rates
Intervention
AT, antithrombin; PC, protein C; PS, protein S; RPL, recurrent pregnancy loss; IUGR, intrauterine growth restriction; VTE, venous thromboembolism; APS, antiphospholipid syndrome; LA, lupus
anticoagulant; aCL, anticardiolipin; UFH, unfractionated heparin; LMWH, low molecular weight heparin.
Carp et al
(2003)
APS (LA or aCL antibodies)
F5 R506Q/F2 mutation or AT/PC/PS deficiency
RPL (defined as 2 consecutive losses <20 weeks’
gestation) or stillbirth/oligohydramnios/IUGR/
previous VTE or family history of thrombophilias
Inherited thrombophilias as above RPL ( 3
consecutive losses in 1st or 2nd trimesters)
Ogueh et al
(2001)
Exclusion criteria
Subject inclusion criteria
Authors
Table III. Studies of anticoagulant and antiplatelet-based treatment that included women with inherited thrombophilia and recurrent pregnancy loss.
Review
537
Review
treatment was associated with a three-fold improvement
with live birth rates of 29% and 86% respectively (Gris et al,
2004). While the outcome with LMWH initially appears
striking, it should be noted that there was no placebo group
and the study included only women who had a single prior
loss. However, perhaps most importantly the live birth rate
in the aspirin only group was much lower than would be
expected with best supportive care. It is therefore not clear
why the group receiving aspirin had such a poor success rate.
This is especially pertinent since it is common clinical practice to give women at risk of poor pregnancy outcome aspirin prophylactically.
To investigate the effect of using two different doses of
LMWH a multi-centre study examined women with RPL
(defined as three or more losses in the first trimester, two or
more in the second trimester or one fetal loss in the third
trimester) and a wide range of thrombophilic defects, including aPL antibodies (20% of total). Pregnancy outcomes following LMWH at low (40 mg enoxaparin, n = 89) and high
doses (80 mg enoxaparin, n = 91) were assessed with 84%
and 78% live birth rates respectively (Brenner et al, 2005).
The relevance of these results to clinical practice is unclear as
there is no comparison to a placebo group.
VTE treatment doses of UFH, LMWH or vitamin K antagonists (between weeks 16 and 36 only due to teratogenicity in
the first trimester) started at positive pregnancy testing
(n = 45 pregnancies from 26 women) were compared to no
treatment (n = 19 pregnancies from 11 women) with a superior live birth rate in the former group of 98% vs. 42%
(Folkeringa et al, 2007). However the applicability of this
non-randomized study is uncertain as the women (with either
AT, PC or PS deficiency) were selected from a previously
designed observational family cohort study assessing risks of
VTE rather than being recruited specifically to assess outcomes after pregnancy loss. Of particular importance is that
only 5% (2 out of 37 women) had prior pregnancy losses.
To date, there are only two well-conducted placebo-controlled trials investigating the use of anticoagulation in RPL,
although neither focused exclusively on women with thrombophilia. Interestingly, compared to the less well designed
smaller studies described above, neither demonstrated a benefit of anticoagulation over placebo for live birth rate (Clark
et al, 2010; Kaandorp et al, 2010). The ALIFE (Anticoagulant
for Living Fetus) study compared placebo to aspirin alone
and aspirin in combination with LMWH, (nadroparin
2850 iu) and showed similar live birth rates of 67%, 62%
and 70% respectively (Kaandorp et al, 2010). In comparison,
the SPIN (Scottish Pregnancy Intervention) study demonstrated a live birth rate of 78% in the combination arm
(aspirin and enoxaparin 40 mg) and 79% in the placebo arm
(Clark et al, 2010). A particular strength of these studies is
the large numbers of women enrolled (almost 100 in each
arm of the ALIFE study, and 150 in each arm of the SPIN
study). Both trials included women with a minimum of two
prior losses and with a low prevalence for F5 R506Q or the
538
F2 mutation of 6·9% and 3·5% in each study respectively. In
the ALIFE study (Kaandorp et al, 2010), previous live births
were documented in 43·1%, 37·5% and 38% of women in
the combination treatment, aspirin only and control groups
respectively. The SPIN study reported 45·6% and 44·9% of
women with prior live births in the combination treatment
and control groups respectively (Clark et al, 2010). No definite conclusion could be reached by either study as to
whether or not anticoagulation in this subgroup of women
with thrombophilia is advantageous. At the very least, the
prevalence of F5 R506Q and the F2 mutations in these studies being equivalent to the general population suggests that
these thrombophilias are not a major feature in these
women. These trials also confirm that women are willing to
take part in placebo-controlled trials of potentially helpful
interventions in pregnancy.
In summary, while both the ALIFE and SPIN studies support the view that LMWH should not be used indiscriminately, the question of whether or not prophylactic
anticoagulation is beneficial in thrombophilic women
remains unanswered.
Current guidelines for managing women with
recurrent pregnancy loss and thrombophilia
Recent guidance on investigation and management of women
with RPL was issued by the RCOG and the American College
of Obstetricians and Gynecologists (ACOG) and reflects the
lack of an evidence base in favour of thrombophilia testing
and anticoagulant-based interventions (Lockwood & Wendel,
2011; Regan et al, 2011). The RCOG Green-top Guideline
(No.17) on investigation and treatment of women with recurrent first-trimester miscarriage and second-trimester miscarriage recommends testing for aPL antibodies; a weaker
recommendation is the screening of women with secondtrimester miscarriage for inherited thrombophilias (Regan
et al, 2011). The ACOG practice bulletin on inherited thrombophilias in pregnancy however does not recommend testing
for inherited thrombophilia in this population because of the
unclear benefits of anticoagulation (Lockwood & Wendel,
2011). The RCOG guidance, in line with well-established
practice, recommends consideration of low dose aspirin and
heparin for pregnant women with APS. In women with inherited thrombophilia, it is thought that there is insufficient evidence to evaluate the benefits of heparin in those with
recurrent first-trimester loss but recommend, on the basis of a
single prospective randomized study that heparin might benefit those with second-trimester miscarriage (Gris et al, 2004).
Conclusion
The contemporary expectations of women to successfully
reproduce, particularly at an increasingly advanced age,
means the demand to provide solutions for pregnancy failure
is greater than ever. As a result, progressively extensive
ª 2012 Blackwell Publishing Ltd
British Journal of Haematology, 2012, 157, 529–542
Review
testing is being performed leading, on many occasions, to
results of questionable value. This vulnerable patient group is
often eager to try any intervention and unless they are fully
informed of the evidence it may be difficult for them to
accept ‘no treatment’. Furthermore, both aspirin and heparin
appear to be safe in pregnancy, so doctors are willing to prescribe them in the hope of some benefit. Given that most
women with unexplained pregnancy loss will go on to have
subsequent successful outcomes with supportive therapy
alone, indiscriminate thrombophilia testing and anticoagulation should be avoided and efforts focused on developing an
evidence-based approach through collaborative and welldesigned multi-centre studies.
APS is the one thrombophilia that has strong data linking
it to poor pregnancy outcomes, albeit that proposed mechanisms are increasingly heterogeneous. The body of data that
suggests the use of aspirin and heparin, whether UFH or
LMWH, to be beneficial to subsequent pregnancy outcomes
is still controversial and further research to strengthen these
data would provide reassurance that appropriate, efficacious
treatments are being used. Conversely, a convincing link
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