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GESTATIONAL AGE-SPECIFIC AMNIOTIC FLUID INDICES IN NORMAL FILIPINO PREGNANCIES
Karen M. Faustino, M.D., Maria Regina P. Manahan, M.D.
Makati Medical Center, Philippines
INTRODUCTION
A correlation between amniotic fluid volume and
gestational age has been established but
differences in environment and race are factors
that may influence this correlation.
The objectives of this retrospective study are (1)
to obtain gestational age-specific amniotic fluid
indices (AFI) in a Filipino population and
compare with Taiwanese, Chinese, Vietnamese,
and North American subjects to determine if
there are significant differences; (2) construct a
table of values and plot predicted percentiles of
AFI per gestational age.
METHODS
Data were gathered from 3,500 Filipinos with
singleton uncomplicated pregnancies from 24 to
41 weeks who underwent sonography at the OBGYN Ultrasound Section of a tertiary institution
from January 2001 to December 2005.
Examinations were performed using a linear
array transducer on B-mode. The AFIs were
measured using the four-quadrant technique.
The AFIs were stratified by gestational age. The
mean and median for each completed week were
calculated, then compared with other populations.
SAS software was used for statistical analyses.
Quadratic regression of mean AFIs was used to
predict the 3rd, 5th, 10th, 50th, 90th, 95th, and 97th
percentiles of AFI per gestational age.
RESULTS
The mean AFI of our subjects peaked at 14.86
cm at 28 weeks then gradually declined until 41
weeks.
Comparing the Filipino with Taiwanese and
Vietnamese populations, majority of the mean
AFIs per gestational age have significant
differences. Thirteen of the eighteen weekly
mean AFIs in the Filipino-Taiwanese comparison,
and eleven of fourteen in the Filipino-Vietnamese
comparison were statistically different.
The North Americans had a slightly higher AFI than
Filipinos, with an average difference of 0.64 cm.
The Chinese had a markedly lower AFI, with an
average difference of 3.59 cm.
Quadratic regression of the mean gestational-age
specific AFIs was used to obtain a best-fit line to
plot predicted values for the 3rd, 5th, 50th, 95th and
97th percentiles. These lines provide a better
estimation of the periodic changes in AFI.
CONCLUSION
The authors recommend usage of the predicted
values obtained in this study as reference AFI for
Filipino patients. There are significant differences
in values across populations, increasing the value
of a race- and gestational age-specific reference.
1 Lu SC, Chang CH, Yu CH, Chang FM. Reappraisal of normal amniotic fluid index in an Asian population:
analysis of 27,088 records. Taiwan J Obstet Gynecol 2007; 46 (3): 260-263.
2 Hinh ND, Ladinsky JL. Amniotic fluid index measurements in normal pregnancy after 28 gestational weeks.
Int J Gynaecol Obstet 2005; 91: 132-136.
3 Lei H, Wen SW. Normal amniotic fluid index by gestational week in a Chinese population. Obstet Gynecol
1998; 92: 237-40.
4 Moore TR, Cayle JE. The amniotic fluid index in normal human pregnancy. Am J Obstet Gynecol 1990; 162:
1168-73.
Address correspondence to Dr. Karen Faustino,
Philippine Children’s Medical Center, Quezon City, Philippines.
Email: [email protected]