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4.1: Pregnancy and Childbirth

Difficulty Level: At Grade Created by: CK-12
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What happens to the mother and child during pregnancy?

Pregnancy results when a fertilized ovum implants in the wall of the uterus and continues to develop. A typical pregnancy begins with conception and ends about 296 days later with childbirth.

Did You Know?

A single act of intercourse at the time of ovulation has a 20% chance of resulting in pregnancy. Most fertile couples achieve pregnancy within six months of trying.

Fertilization occurs when a sperm unites with an egg. This typically occurs inside the ovarian end of the Fallopian tube where sperm coming from the uterus meet the egg moving towards the uterus.

There is a limited period of time during which conception may occur. The egg stays alive for 12 to 24 hours after it leaves the ovary. Sperm usually survive in the vagina for about 24 hours after ejaculation (although some may stay alive for up to three days). Therefore, for a woman to get pregnant, sexual intercourse should take place within a day before or two days after ovulation. So the total fertile period each month is up to three days.

Figure 3.1 Path of the sperm through male genitalia.

Figure 3.2 Path of sperm in the uterus and Fallopian tubes.

Fertilization Math How long might it take for a sperm to reach an egg? Use the following assumptions.

  • Fallopian tubes are 4 inches long.
  • Ovum is pushed along by cilia at the rate of 1 inch per day.
  • Intercourse occurs at the time that the egg leaves the follicle (ovulation).
  • Uterus is 3 inches long and 2 inches wide.
  • Sperm travel at a rate of .08 inches per minute.

Activity 3-1: The Journey of the Sperm and the Egg


You are an editor for a scientific journal. An author was asked to write an essay describing the journey of the sperm and egg. However, the author never learned the correct scientific terminology, so the essay is incomplete. It is your job to complete this essay using the correct terminology.


  • Activity Report


Step 1 You will receive an activity sheet showing both the male and female reproductive systems.

Step 2 Follow the instructions on the activity sheet.

Did You Know?

Sperm contain three parts-head, middle, and tail. The head contains all of the genetic material. The middle part has the energy pack that propels the tail that moves the sperm.

Figure 3.3 The journey of a fertilized egg from the Fallopian tube to the uterus takes about one week.

Journey of the Fertilized Egg

As shown in Figure 3.3, the fertilized egg gradually moves through the Fallopian tube toward the uterus. While on its way, the fertilized egg begins to divide, first into two cells, then into four cells, then eight cells, and so on. By the end of a week, when it reaches the entrance to the uterus, it has become a cluster of cells that implants or lodges in the uterine wall called the endometrium. The cluster of cells is now a growing organism called an embryo. It will be called an embryo for the first eight weeks of intrauterine development. After eight weeks, the embryo is called a fetus. We will explore the development of the fetus in the next section. In this section you will discuss pregnancy as an expectant mother experiences it.

If sperm moving up the uterus to the Fallopian tubes don't know which tube has an egg in it, what percent chance does each sperm have of choosing the right tube?

Did You Know?

Pregnancy tests recognize special chemicals called hormones that are produced during pregnancy. The implanted embryo provides one such hormone. Sometimes these hormones are present in abnormal conditions. However, this hormone normally occurs only in pregnancy. So if this hormone appears in a healthy woman's urine or blood, it is chemical evidence that she is pregnant.

How does a woman know if she is pregnant? The most commonly noticed sign is a missed menstrual period. Since menstrual periods are not always regular, a period may be late by several days or even longer for reasons other than pregnancy. Malnutrition, stress, or long periods of strenuous exercise may cause a late or missed period. Nevertheless, if a woman has had sexual intercourse, and her period is a week or more late, she should take a pregnancy test, either with a home kit or at a doctor's office. If a pregnancy kit is used at home and shows she is pregnant, the woman should begin seeing a doctor.

Figure 3.4 This picture shows what an ultrasound picture of a fetus looks like.

During the first couple of months, a pregnant woman is likely to feel unusually tired. She may experience nausea and vomiting. Since these symptoms are worse in the morning, they are called “morning sickness.” Her breasts may feel swollen and she may need to urinate frequently. By the third or fourth month, her abdomen will begin to swell, and she may feel the fetus move. Most women look forward to hearing the baby's heartbeat, which is usually audible with a special stethoscope by the third or fourth month. Some women also have an opportunity to see their baby through an image generated by an ultrasound machine that uses sound waves to show a picture of the baby on a television monitor (Figure 3.4). Ultrasound is a useful tool in detecting problems with the developing fetus. It also offers parents their first view of the baby. Ultrasound is much safer than X rays.

By the end of the first trimester, or the first three months, the mother is typically free of the symptoms of early pregnancy. Hence, the next three months are usually a more comfortable time. They are also an exciting time as the mother starts to feel the fetus moving. Women can continue working and taking part in gentle exercise like swimming and walking throughout the second trimester quite comfortably. Some women exercise up to the day their babies are born.

Did You Know?

Among mammals, the opossum has the shortest pregnancy (gestation period) of 14-17 days. The Asian elephant endures the longest pregnancy-645 days!

The third trimester may involve a bit more discomfort as the fetus increases in size. A pregnant woman typically gains a total of 20 to 30 pounds. Of that 20 to 30 pounds, only about 7 to 8 pounds is due to the developing baby. Women who gain excessive weight may experience complications. By the third trimester, a woman often begins feeling impatient and starts to prepare herself for the baby's arrival.

Pregnancy usually progresses normally, but it can have complications that may endanger the mother or the baby. In earlier times, pregnancy and childbirth often caused illness and death. At present, one in 10,000 pregnant women in the United States dies as a result of pregnancy. This average figure is called the maternal mortality rate. The maternal mortality rate varies widely in different groups. Pregnant women who receive good medical care, called prenatal care, early in their pregnancy have a much lower risk of complications than those who do not receive medical care. Good medical care encourages healthy eating habits, exercise, and the avoidance of drugs and alcohol. In addition, women receive lots of information about themselves and their baby, which prepares them for motherhood.

Pregnant adolescents are generally less likely to receive good care, especially if they are poor. Many pregnant teenage girls fear and deny being pregnant. They often do not see a physician until there is a problem. Prenatal care is expensive, and those without insurance coverage to help pay for office visits don't go. Also, some adolescent girls who get pregnant engage in high-risk behavior (besides having unprotected sexual intercourse, which always carries the risk of pregnancy) such as drinking alcohol or taking drugs. Since drugs and alcohol can cause a number of complications for the baby before and after birth, it is even more important than usual to avoid drugs and alcohol during pregnancy. Prenatal care can make a big difference. Prenatal care educates an expectant mother about, and often helps her to change, any behaviors that may be harmful to her and her baby.

If a woman suspects she is pregnant, she should see a doctor as soon as possible to confirm the pregnancy and to begin receiving the guidance and care that is necessary to safeguard her health and the health of her developing baby.

In addition to laboratory tests, a woman can use a pregnancy-testing kit available at drugstores for home use. These tests can detect pregnancies as early as nine days after a missed period. If a test is repeated a week later, the results are accurate about 90% of the time.

Embryonic Models Using paper, clay, string, or any materials you think will work, construct life-size models of the embryo/fetus at various stages of development.

The Development and Birth of the Baby

Now let's turn to the development of the baby. At the time of implantation, the embryo is no larger than a tiny dot, about the size of the period at the end of this sentence. However, at implantation the embryo is more than just a jumble of cells. By the third week of life, its cells have organized into three layers. The parts and systems of the body grow out of these three layers. At one month, the embryo is no bigger than the nail of your finger, yet it already has a tiny heart, a growing brain, and the beginnings of eyes and ears (Figure 3.5). The sex of the embryo, however, is not yet apparent from the genitals. By the end of eight weeks, all of the essential organs are in place but will continue to grow and mature.

Fetal Development during the First Three Months (First Trimester)

During first month

  • Heart starts beating.
  • Blood begins to circulate.
  • Brain begins to form.
  • The eyes and ears begin to form.

During second month

  • Arms, legs, and internal organs take shape.
  • All organs are in place.
  • Basic human form begins to appear.

During third month

  • Male and female genitalia look different.
  • Fingers, toes, and nails form.
  • Sense organs develop.

Figure 3.5 Embryonic development during the first three months.

From eight weeks on, the development of the fetus is mainly a matter of further growth in size and maturation in function. No new parts develop-everything is already in place. At three months, the fetus is still small enough to fit in an adult's hand, but it can swallow and bend its fingers. By four months, all of the major organs are well formed and the fetus looks like a tiny baby (Figure 3.6).

The fetus grows in a sac full of fluid, called amniotic fluid. The amniotic fluid provides extra protection against physical injury. The fetus depends completely on the mother for sustenance. The umbilical cord is the fetus's lifeline to the mother. It connects the circulatory system of the fetus to that of the mother through the placenta.

The placenta grows from fetal and maternal tissues into an organ that weighs about one pound. It is lodged in the wall of the uterus at the site of implantation. Within the placenta, oxygen and nutrients in maternal blood pass into fetal blood. At the same time, carbon dioxide and waste products in fetal blood pass into the maternal blood and are carried away.

Figure 3.6 Fetus at 19 weeks, 8 inches (actual size).

The exchange of wastes and nutrients between maternal and fetal blood takes place through the walls of tiny blood vessels called capillaries. Maternal and fetal blood do not come in direct contact or mix with each other. Body functions normally performed by breathing, digesting foods, and getting rid of wastes are carried out for the fetus by the mother's body.

Fetal Development during the Second Three Months (Second Trimester)

During fourth month

  • Muscles move.
  • Facial features form, including eyebrows and eyelashes.
  • Reacts to sounds.
  • Hair covers body.

During fifth month

  • Fetal movement can be felt by mother.
  • Heartbeat can be heard.

During sixth month

  • Brain waves begin.
  • Eyes open.
  • Fingerprints and footprints form.

Fetal Development during the last Three Months (Third Trimester)

During seventh month

  • Adds body fat.
  • Moves around a lot.
  • Experiences periods of being awake and asleep.

During eighth month

  • Grows taller and heavier.
  • Nails and bones begin to harden.

During ninth month

  • Organs mature.
  • Can best survive outside uterus.

Figure 3.7 A baby at full term.

What Do You Think?

Why might some people prefer to give birth in their own home with a midwife attending, instead of giving birth in a hospital?

It takes about nine months for the human fetus to become fully mature (Figure 3.7). Babies born before eight months are usually considered premature. Prematurity is not only a question of time, but also a matter of weight. Babies usually weigh a little over 7 pounds, but they can be quite a bit heavier or lighter. Do you know how much you weighed at birth? A baby who weighs less than 5 pounds 8 ounces (2,500 grams) is considered premature. Most premature babies can survive only with special medical care. But the limit for viability, the ability to survive outside the mother's body, is about six months, which is at the end of the second trimester. Fetuses usually weigh about 2.2 pounds at this time.

Why do you have a belly button or a navel?


Toward the end of the seventh month, most babies are in an “upside-down” position with their heads pointing towards the cervix (see Figure 3.7). As the time of childbirth approaches, the mother begins to experience occasional contractions of her uterus. When these contractions become strong and regular, the mother has entered labor, the process of bringing the fetus from inside the uterus out into the world. With each contraction, the uterine muscles push the fetus down, the lower part of the uterus, opening the cervix to let the baby through (Figure 3.8).

Figure 3.8 Steps in a normal birth.

What Do You Think?

Can you control what sex child you have?

Soon after birth, the baby's lungs expand, and it is no longer dependent on the placenta for oxygen and nutrients. A new person has now joined the world.

  • Why is it even more important than usual for a woman to not smoke, drink, or use drugs when she is or may become pregnant? Why are the first three months of pregnancy so critical?
  • Why are most babies in an “upside-down” position in the uterus? Why is it easier for a baby to be born headfirst?
  • How do twins occur?

Activity 3-2: Boy or Girl?


Throughout history, it was a common misconception that women somehow determined the sex of the child. For example, Henry VIII (king of England in the 16th century) blamed his wives for not producing a male heir. He divorced two wives and even beheaded two. Perhaps if King Henry did the following activity, he would have been a more understanding husband!

All eggs contain an X chromosome. A sperm can contain either an X chromosome or a Y chromosome. When the egg and the sperm unite, the sex of the child is determined by the X and Y chromosomes present. If there are two X chromosomes, the child will be a girl. If there is an X chromosome and a Y chromosome, the child will be a boy. Since all eggs contribute an X chromosome, the sex of the child is actually determined by the father's sperm, which can contain either an X or a Y chromosome.


  • Coin to toss
  • Activity Report


Step 1 Pair with a partner.

Step 2 Study Figure 3.9 before beginning this activity.

Figure 3.9 X and Y chromosomes determine the sex of a child.

Step 3 Tossing a coin, determine what the chances are that a baby will be a boy or a girl by using heads to represent an X sperm and tails to represent a Y sperm. Record each toss of the coin.

Step 4 The result from each partnership will be added together and announced to the class.

You are a fetus with exceptional communication skills. Write a letter to your mother. In your letter, express your concerns regarding the pregnancy and how you want her to take care of herself and you. Tell her about the changes you are going through, and how you are feeling about the prospect of being born.

Review Questions

  1. What happens to a fertilized egg while traveling to the uterus? How long does the journey take?
  2. What are some signs and symptoms of pregnancy?
  3. Why is prenatal care important?
  4. By the time the fetal heartbeat can be heard, what developments have taken place in the fetus?
  5. What determines the baby's viability if it is born prematurely?
  6. What is the placenta? Why is it important?
  7. What does labor mean?

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