21 Learning About Pregnancy and Childbirth

What You’ll Learn
1. Explain how a baby is
conceived and how the baby’s
sex and inherited traits are
determined. (p. 243)
2. Explain how pregnancy is
determined. (p. 246)
3. Explain why prenatal care is
important. (p. 248)
4. Describe the three stages
of labor. (p. 250)
Learning About
Pregnancy and
• I will learn about pregnancy and childbirth.
nowing about the human body also entails learning about conception and childbirth. In this lesson, you will learn about heredity
and the process of development. You will discover facts about
the way a cell grows
and develops into
a human being.
Why It’s Important
The understanding of growth and
development begins with
pregnancy. Understanding how
pregnancy occurs and the
importance of a healthy
pregnancy is an important step in
a healthy development
throughout the life cycle.
Key Terms
fetal alcohol syndrome (FAS)
242 UNIT 4 • Growth and Development
Rubberball Productions/Photodisc/Getty Images
Writing About Parenthood Suppose your aunt and uncle announce
that they are having a baby. Your aunt wants to keep taking a certain
prescription medication during her pregnancy. She does not think it is
important to tell her physician what she wants to do. After reading the
information about prenatal care on pages 248 and 249, write an entry in
your health journal about what you might advise your aunt to do.
he union of an ovum and a sperm is conception, or fertilization. One
ovum matures and is released from an ovary each month. Once an ovum is
released, it enters a Fallopian tube (sometimes called an oviduct). As the
ovum moves through the Fallopian tube, it can be fertilized if sperm are present.
Conception usually occurs in the upper-third portion of a Fallopian tube.
What to Know About Conception
and Heredity
Chromosomes in men and women In
a female, the 23 pairs of chromosomes are identical. In a male, one
pair of chromosomes is not made up
of identical chromosomes.
In both males and females, one
pair is called the sex chromosomes.
In females, the pair of sex chromosomes is identical and is called XX.
Every ovum produced by a female
contains an X chromosome.
In males, the pair of sex chromosomes is not identical and is called
XY. Sperm produced by a male contain either an X chromosome or a Y
chromosome which determines a
baby’s sex.
The presence of a Y chromosome is
essential for the development of male
characteristics and the presence of an
X chromosome is essential for the
development of female characteristics.
The sex of a baby is determined by the
sex chromosome from the father. When
a sperm fertilizes an ovum, a full complement, or set, of 46 chromosomes (23
from the father and 23 from the
mother) is present in the resulting cell.
At conception, heredity is determined. Heredity is the passing of
characteristics from biological parents to their children. All body cells,
except sperm and ova, contain 23
pairs of chromosomes. A chromosome is a threadlike structure that
carries genes. A gene is a unit of
hereditary material.
The sex of a baby is
determined by the
possible combinations
of the X and Y
LESSON 21 • Learning About Pregnancy and Childbirth 243
Chromosome Count
Some genetic
disorders are the
result of abnormal
chromosome numbers.
Down syndrome, for
example, involves an
extra chromosome.
A dominant gene
influences a child’s
If a sperm with an X chromosome
fertilizes an ovum, the resulting cell
will have an XX pair of sex chromosomes. A fertilized ovum with an XX
set of chromosomes develops into a
female. If a sperm with a Y chromosome fertilizes an ovum, the resulting cell will have an XY pair of sex
chromosomes. A fertilized ovum with
an XY set of chromosomes develops
into a male.
Genes All chromosomes carry genes
that contain hereditary material.
Sex-linked characteristics are hereditary characteristics that are transmitted on the sex chromosomes. For
example, the X chromosome carries
genes for traits such as color vision
and blood clotting. The Y chromosome does not carry matching genes
for those or other traits. Therefore,
when the X and Y chromosomes are
present together, the genes on the X
chromosome control those traits.
Inherited characteristics Inherited
characteristics are determined by
genes carried on chromosomes.
Genes are arranged on chromosomes
somewhat like beads on a necklace.
Just as chromosomes are paired, so
are genes.
There are two genes for every trait.
One is located on each chromosome
that makes up a pair.
If the maternal and paternal genes
for a trait are different, one will override the other. A dominant gene is a
gene that overrides the expression of
the other gene. A recessive gene is a
gene whose expression is overridden
by the other gene.
For example, a paternal gene for
brown eyes might line up with a
maternal gene for blue eyes. In this
case the gene for brown eyes will
keep the gene for blue eyes from
being expressed.
The gene for brown eyes is dominant. The gene for blue eyes is recessive because it is not expressed when
the dominant gene for eye color is
If an offspring inherits recessive
genes for eye color from both parents,
the offspring will have blue eyes.
Other examples of dominance in
humans are curly hair over straight
hair and dark hair over blond hair.
Genetic counseling A couple may
receive genetic counseling to prepare
for parenthood. In some cases, a
physician may recommend that a
pregnant female have a test for possible genetic defects. Genetic
counseling is a process in which a
trained professional interprets medical information concerning genetics
to prospective parents.
244 UNIT 4 • Growth and Development
Mike Bluestone/Photo Researchers
Ultrasound examination is
a painless procedure.
Amniocentesis (am nee oh sen
TEE suhs) is a diagnostic procedure
in which a needle is inserted through
the uterus to extract fluid from the
amniotic sac. The amniotic sac is a
pouch of fluid that surrounds a fetus.
The extracted fluid contains valuable
genetic information about the fetus.
Cells extracted from the amniotic
fluid are analyzed to determine if any
genetic defects are present. The sex
of the fetus also may be revealed.
If necessary, the procedure is performed in the second trimester of a
pregnancy. Amniocentesis usually is
safe for both the mother and the
fetus. It is recommended for women
over 35 and women who are at risk
for giving birth to a baby with
genetic or chromosomal disorders.
Ultrasound is another diagnostic
procedure used to monitor the fetus.
With ultrasound, high-frequency
sound waves are used to provide an
image of the developing baby. Then,
the physician evaluates the image.
Ultrasound can be used to confirm
pregnancy and to confirm that the
pregnancy is within the uterus, rather
than in the Fallopian tube (a condition
known as an ectopic pregnancy).
Ultrasound also can be used to assess
the size and growth of the fetus and to
help a doctor diagnose any problems
the mother might be having.
This ultrasound procedure often
takes place in the first trimester of a
pregnancy. Further ultrasounds during the pregnancy help monitor the
growth of the fetus.
The procedure is safe for both the
mother and the fetus. With ultrasound, some problems can be diagnosed before birth and some can even
be treated while the fetus is still in
the uterus.
Ultrasound also reveals the sex of
the fetus and if there is more than
one fetus in the uterus. Knowing
ahead about the presence of a birth
defect is helpful in planning how to
care for the baby after birth.
Make the
Body Systems For
more information
on the female
reproductive system,
see page 228 in
Lesson 20.
1. What determines
the sex of a baby?
2. How does a
dominant gene
differ from a
recessive gene?
3. How does
differ from
LESSON 21 • Learning About Pregnancy and Childbirth 245
Mike Bluestone/Photo Researchers
fter conception, a fertilized ovum continues to divide and move
through the Fallopian tube. The cell divisions form a cluster of cells
by the time they reach the uterus. These cells attach to the
endometrium, which is the lining of the uterus. An embryo is a developing
baby through the second month of growth after conception. A fetus is a
developing baby from the ninth week after conception until birth.
What to Know About Pregnancy
Eating Habits Poor
eating habits before
and during a
pregnancy can harm
both the mother and
the fetus.
The outer cells of the embryo and the
cells of the endometrium form the
placenta. The placenta is an organ
that anchors the embryo to the
uterus. Other cells form the umbilical
cord. The umbilical cord is a ropelike structure that connects the
embryo to the placenta. The mother’s
blood carries nutrients and oxygen to
the embryo or fetus through the
umbilical cord until birth. Waste
products from the embryo move
through the cord to the mother’s
bloodstream to be excreted.
How pregnancy is determined The
first sign that indicates pregnancy is
the absence of a menstrual period.
However, a missed period does not
always indicate pregnancy. A female
may skip her menstrual period
because of stress, diet, physical activity, or illness.
If conception has occurred, a
female usually has other symptoms
of pregnancy. She may have excessive
tenderness in her breasts, fatigue, a
change in appetite, and morning sickness. Morning sickness is nausea and
vomiting during pregnancy. Some
pregnant females have spotting or
light, irregular menstrual flow.
A female who misses a period and
also has other symptoms of pregnancy
246 UNIT 4 • Growth and Development
Photodisc/Getty Images
should have a pregnancy test. This
test is used to detect a hormone that
is present a few days after fertilization. A physician or nurse practitioner can administer this test and
send it to a lab for confirmation.
Some home pregnancy tests also
are sold in drugstores. Home pregnancy tests may not always be reliable soon after a missed period. A
pregnancy should always be confirmed by a physician or a nurse.
Pregnancy usually lasts nine
months. Each nine-month period is
divided into trimesters or three-month
Umbilical cord
A fetus is well-nourished
and protected in the uterus.
The first trimester The first three
months after conception are the first
trimester. At the end of the first
month, the embryo has a heartbeat, a
two-lobed brain, and a spinal cord.
By the end of the second month,
the embryo is recognizable as a
human and is called a fetus. After
two months, the embryo has started
to form arms and legs as well as fingers, ears, and toes. The fetus can be
visibly identified as a male or female.
By the end of the first trimester, the
heart has four chambers.
The second trimester By the end of
the fourth month, fingernails, toenails, eyebrows, and eyelashes have
developed. Teeth begin to form, lips
appear, and head hair may begin to
grow. Movement of the fetus can be
felt by the mother. The fetus can bend
its arms and make a fist. During the
fifth month, the heartbeat can be
detected by a stethoscope.
The third trimester If a baby is born
prematurely at the beginning of the
seventh month, it has a 20 percent
chance of surviving. Optimum development occurs at about 40 weeks
after conception.
A premature birth happens when
a baby is born before 37 weeks of
pregnancy. A premature baby has not
had time to fully develop all body
systems. For example, underdeveloped lungs are a usual problem in
premature babies.
A baby born between 38 and 40
weeks of pregnancy is considered to
be full-term. Full-term babies usually
are 19 to 21 inches long and might
weigh between six and nine pounds
by the end of the third trimester.
The embryo in this photo
is less than 1 inch long.
By the end of the first
trimester, the fetus is about
three inches long and
weighs about an ounce.
By the end of the second
trimester, the fetus is about
12 inches long and weighs
about one pound.
By the end of the third
trimester, the baby is ready
to be born.
1. What is the
function of the
umbilical cord?
2. During which
trimester can the
fetus be identified
as a male or
LESSON 21 • Learning About Pregnancy and Childbirth 247
(t)Lennart Nilsson/Albert Bonnier Forlag AB, (c)Lennart Nilsson/Albert Bonnier Forlag AB, (b)Petit Format/Photo Researchers
he care that is given to the mother and baby before birth is prenatal care. Prenatal
care includes routine medical examinations, proper nutrition, reasonable exercise, extra
rest and relaxation, childbirth and child-care education, avoidance of drugs and other
risk behaviors, and the practice of common sense.
What to Know About Prenatal Care
Babies born prematurely
need very special care.
A well-balanced diet is important to a
pregnant female. Premature birth or
low birth weight may result when a
developing baby does not receive
adequate nutrients.
Premature birth is the birth
of a baby before it is fully developed—less than 37 weeks from
the time of conception.
A low birth weight is a weight at
birth that is less than 5.5 pounds.
Premature birth and low birth
weight are associated with mental
disability and infant death.
A pregnant female needs to check
with her physician before she takes
any prescriptions or over-the-counter
drugs. Drugs present in the mother’s
bloodstream can pass into the devel-
248 UNIT 4 • Growth and Development
(tt)Doug Martin, Beaver English Studio, Photodisc/Getty Images; (b)Edwige/Photo Researchers
oping baby’s bloodstream and harm
the baby. For example, tranquilizers
taken early in pregnancy can cause
birth defects. Some drugs prescribed
for acne and hormones, such as those
in birth control pills also can cause
birth defects. Aspirin may interfere
with blood clotting in both the pregnant female and her developing baby.
A female should not drink alcohol
during pregnancy. Fetal alcohol
syndrome (FAS) is the presence of
severe birth defects in babies born to
mothers who drink alcohol during
pregnancy. FAS includes damage to
the brain and to the nervous system,
facial abnormalities, small head size,
below normal I.Q., poor coordination,
heart defects, and behavior problems.
A pregnant female should not
smoke or inhale smoke from tobacco
products. Females who smoke have
smaller babies who are more unhealthy than babies of nonsmoking
females. Babies born to mothers who
smoke also may be at risk for heart
disease in adulthood. Smoking and
breathing smoke increase the risk of
complications, miscarriage, and stillbirth during pregnancy.
A miscarriage is the natural ending of a pregnancy before a baby is
developed enough to survive on its
own outside the mother’s body. A
stillbirth is the birth of a dead fetus.
Accessing Valid Health Information, Products, and Services:
Research a Pregnancy Topic
There are many sources available for information about pregnancy. To be a good researcher, you will
need to look through multiple sources of information to ensure that you get all the facts.
Evaluate the information. If you are using your research to write a paper, be sure to cite your sources.
Find health information,
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A pregnant female should not use
other harmful drugs, such as marijuana, crack, cocaine, or heroin.
Babies born to mothers who use
these drugs can be born prematurely
and have low birth weight. These
babies may be born addicted to
Some research indicates that caffeine may be linked to birth defects.
Caffeine is found in coffee, chocolate,
cola drinks, tea, and some prescription and over-the-counter drugs. A
mother-to-be should follow her physician’s advice about caffeine.
One nutrient known to prevent
birth defects is folic acid. Folic acid is
the chemical form of folate, which is
found in green leafy vegetables, citrus fruits, and legumes. Folate aids in
cell division, and consuming foods
high in folate reduces a woman’s
chance of having a child with spina
bifida and other abnormalities of the
spine and brain.
The U.S. Public Health Service recommends that all women of childbearing age, who are capable of
becoming pregnant, consume 0.4 mg
of folic acid per day to help prevent
neural tube defects. For pregnant or
lactating women, the daily value
increases to 0.8 mg per day. It is especially important that women consume sufficient folate before they
become pregnant.
Use every resource
available to you to obtain
information on the topic
you have chosen.
1. What is prenatal
2. What is fetal
alcohol syndrome
LESSON 21 • Learning About Pregnancy and Childbirth 249
Laura Sifferlin Photography
he process of childbirth is called labor. During labor, muscular
contractions of the uterus start, become more intense, last longer, and
become more frequent. The amniotic sac may rupture shortly before or
after labor begins. A discharge or gushing of water from the vagina indicates
the sac has broken. Bloody show, which is the discharge of the mucous plug that
sealed the cervix during pregnancy, also may be experienced.
What to Know About Childbirth
Labor is considered to have three distinct stages.
Stage 1: Dilation of the cervix The
first stage of labor is the longest
stage. The length of this stage varies
considerably. It can last from two
hours to many hours. Dilation or
widening of the cervix occurs. The
cervical opening enlarges eight to ten
centimeters—wide enough for the
baby to move through.
Stage 2: Delivery of the baby The second stage begins when the cervix is
completely dilated and ends with the
The cervix begins to dilate during the first
stage of labor.
250 UNIT 4 • Growth and Development
delivery of the baby. The baby moves
farther down the birth canal, usually
head first. The mother pushes, and
the muscles in the uterus contract to
push the baby out.
Crowning is the appearance of
the baby’s head during delivery. Once
the baby has been eased out of the
birth canal and begins to breathe on
its own, the umbilical cord is cut.
Stage 3: Delivery of the placenta The
third stage of labor is the expulsion of
the afterbirth. The afterbirth is the
placenta that is expelled after delivery. If this does not occur naturally,
the physician removes it.
The baby moves down the birth canal and is
born during the second stage of labor.
When the baby is breathing on its
own, the umbilical cord is clamped
and cut off. A stump remains on the
navel. It dries up and falls off in a few
days. A physician gives the baby an
Apgar score.
The Apgar score is a rating of
physical characteristics of an infant
at one and five minutes after birth.
Another score is given at 10 minutes
if there are problems with the baby.
Characteristics, such as heart rate,
color, respiratory effort, and reaction
to sucking, are scored and used to
predict the health of the baby. A score
of 7–10 is normal, 4–7 might need
some resuscitative measures, and
3 and below require immediate
The postpartum period is the
span of time that begins after the
baby is born. Hormones produce
changes in the mother’s body. The
breasts secrete a watery substance
believed to provide the baby with
immunity to certain diseases.
The breasts also secrete a hormone
that stimulates the breasts to secrete
milk. Some studies show that breastfed babies have fewer cases of
In the third stage of labor, the uterus
continues to contract to expel the placenta.
respiratory illnesses, skin disorders,
constipation, and diarrhea.
Multiple births Some pregnancies
result in the birth of two or more
babies at the same time. Two babies
born at the same time are called
Identical twins develop from the
same ovum and sperm. Identical
twins develop when one fertilized
ovum divides at an early stage of
development and the two cells divide
and develop separately. This results
in twins of the same sex who have
identical chromosomes and are very
similar in appearance.
Fraternal twins develop when
two ova are released from an ovary
and are fertilized at the same time by
different sperm. The twins may or
may not be the same sex and usually
do not look alike.
Three babies born at the same
time are called triplets, four are
quadruplets, five are quintuplets,
and six are sextuplets. Multiple
births of more than three babies
are rare.
Childbirth classes Childbirth classes
are available to prepare prospective
parents for the birth of their baby.
Hospitals, health centers, and other
organizations offer these classes. The
classes include detailed information
about the process of childbirth. A
nurse or other health-care practitioner is available to answer questions and to help with concerns.
Special exercise classes also are
offered for pregnant females to help
them stay fit during pregnancy and
prepare for childbirth. A female
should obtain permission from her
physician before participating in
exercise classes.
Make the
Healthful Behaviors
For more information
on practicing healthful
behaviors, see page 27
in Lesson 3.
1. What are the three
stages of labor?
2. What is the Apgar
3. What is the
difference between
identical twins and
fraternal twins?
LESSON 21 • Learning About Pregnancy and Childbirth 251
Complications During Pregnancy
and Childbirth
Ectopic pregnancy Ectopic pregnancy, which can be caused by tissue
scarring from STDs, is a pregnancy
that occurs outside of the uterus. The
embryo becomes implanted in the
Fallopian tube or another location in
the abdomen. Symptoms include
cramping, severe abdominal pain,
and spotting. Surgery often is
needed to remove the embryo. An
ectopic pregnancy can be fatal to
In an ectopic
pregnancy, as the
embryo develops, the
Fallopian tube
expands, causing
potentially serious
Rh incompatibility Rh incompatibility is a mismatch between the blood
of a pregnant female and the blood of
the developing baby. The female’s
blood produces an antibody that
attacks a substance in the developing
baby’s blood. Rh incompatibility may
occur when a female’s blood is Rh
negative and the developing baby’s is
Rh positive. The condition can be
treated and an injection of an anti-
Fallopian tubes
body to the Rh factor is given to the
female to prevent risk during future
Toxemia of pregnancy Toxemia of
pregnancy is a condition characterized by a rise in the pregnant female’s
blood pressure, swelling, and leakage
of protein into the urine. Untreated
toxemia can result in the death of the
female or the developing baby.
Miscarriage Miscarriage is the natural ending of a pregnancy before a
baby has developed enough to survive on its own. Miscarriages occur
most often during the first trimester.
They may be caused by a defect in
the fetus or a medical condition of the
fetus or pregnant female. Signs of
miscarriage include cramping, severe
pain, spotting, and bleeding.
Cesarean section Cesarean section is
a procedure in which a baby is
removed from the mother by making
an incision through the mother’s
abdomen and uterus and removing
the baby. A cesarean may be performed if an unborn baby is too large
to pass through the mother’s pelvis,
is not positioned correctly, or the
physician determines that a vaginal
delivery may be dangerous to the
health of the mother or the baby.
Recovery time from a cesarean delivery is longer than recovery from a
vaginal delivery.
Stillbirth Stillbirth is a fully developed baby that is born dead. Stillbirth
may be caused by a defect in the baby
or a medical condition of the baby or
the pregnant female.
252 UNIT 4 • Growth and Development
fetal alcohol
premature birth
Key Terms Review
Explain the relationship between the pairs of lesson Key Terms given below. Do not write in this book.
1. gene—chromosome
6. afterbirth—labor
2. embryo—fetal alcohol syndrome (FAS)
7. embryo—fertilization
3. placenta—afterbirth
8. fetal alcohol syndrome—ultrasound
4. fertilization—labor
9. placenta—embryo
5. amniocentesis—ultrasound
10. amniocentesis—gene
Recalling the Facts
11. Explain why the resulting chromosome
number in a fetus is the same as the
parents’ chromosome number.
15. What is one unique aspect of each
trimester of pregnancy?
12. What are dominant genes? Give two
16. Why is it important to begin prenatal care
as soon as a female finds out she is
13. How are a fetus’ sex and inherited traits
17. How can taking a childbirth class promote
a healthful pregnancy?
14. What are six complications of
18. How can cigarette smoke affect a developing embryo or fetus?
Critical Thinking
19. Why should a female in late pregnancy
seek medical help if the amniotic sac
20. Why is fertilization in a blocked Fallopian
tube dangerous both to the pregnant
female and to the fetus?
21. In what ways is a pregnant female’s
diet important to the health of
the fetus?
22. How are ova and sperm different from
other body cells?
Real-Life Applications
23. What arguments would you use to try to
dissuade a pregnant female from using
harmful drugs?
24. How would you persuade your pregnant sister that her diet has an effect on her fetus?
25. Explain the concerns you might have about
a baby born prematurely.
26. Discuss why a mother and baby are taken
to a hospital even if the baby is born on
the way.
Responsible Decision Making
Write You go to lunch with a family friend
who is pregnant. Several people are waiting
in line for a table. The host explains that you
can have a table right now if you want to sit
in the smoking section. The family friend is
uncomfortable standing. Write a response to
this situation. Refer to the Responsible
Decision-Making Model on page 61 for help.
Visit www.glencoe.com for more Health & Wellness quizzes.
Sharpen Your Life Skills
Use Communication Skills
Warnings on alcohol and tobacco products
describe why it is harmful for pregnant
women to use these products. Draw a picture of a warning label with text that
emphasizes the risks of smoking, being
around second hand smoke, or drinking
during pregnancy.
LESSON 21 • Study Guide 253
Rubberball Productions/Photodisc/Getty Images