Table of Contents
What is Pregnancy
The series of events, extending from CONCEPTION to delivery (CHILDBIRTH), through which a blastocyst (the clump of cells that implants in the endometrium, the lining of the UTERUS) becomes a baby. A full-term pregnancy spans 266 days. However, doctors calculate the estimated date of delivery, commonly called the due date, to be 280 days from the start of the last menstrual period.
Though a missed menstrual period is the classic first sign of pregnancy, URINE pregnancy tests are now sensitive enough to detect minuscule amounts of pregnancy-related hormones in the urine only a few days after conception and well before the woman misses a period. Home pregnancy tests are generally as accurate as the tests health-care providers use, though following the directions precisely is important. False results are common because of mistakes such as using a urine sample other than the first of the day (which is the most concentrated) or not properly timing the duration of the test. Most health-care providers will do a pregnancy BLOOD test at the first prenatal visit to confirm the pregnancy. Pregnancy tests, urine or blood, measure the presence of human chorionic gonadotropin (hCG) or beta hCG.
Early signs of pregnancy a woman may detect include
- tender, swollen breasts
- unexplained nausea and vomiting
- aversions to or cravings for certain foods, including smells and sights of them
- profound tiredness
- sensation of lower abdominal bloating
- increased URINATION
- lightheadedness or dizziness
The health-care provider’s examination also detects signs of pregnancy, including changes in the texture (by internal palpation) and appearance of the CERVIX and an enlarged, softened uterus. As pregnancy advances the uterus rises out of the pelvis and into the abdomen (beginning around 12 weeks). As part of the diagnostic process the provider uses terminology to identify how many pregnancies and how many deliveries the woman has had previous to the current pregnancy, designating them with the Latin words gravida and para. A woman who has been pregnant twice and delivered twice is a gravida 2 para 2, for example, and a woman who is pregnant for the first time is a primigravida nullipara or gravida 1 para 0.
Key Changes During Pregnancy
The woman’s body undergoes profound changes during the course of pregnancy. Hundreds of hormones unique to pregnancy initiate and facilitate these changes, the most obvious of which are enlarged breasts and a steadily expanding belly. This biochemical flood is also responsible for the emotional swings that characterize early pregnancy. Nearly every body system modifies its functions in some fashion to support the pregnancy and the developing FETUS.
Uterus and abdomen
The woman’s uterus, pelvis, and abdominal structures flex and expand to accommodate the fetus as it develops and grows. The uterus, for example, can stretch up to 10 times its normal size during pregnancy. The numerous hormones unique to pregnancy act on connective tissue throughout the woman’s body to soften ligaments and muscles, providing the pliability necessary to allow this expansion. This softening also accounts for the MUSCLE and JOINT aches, especially in the hips and knees, common in the last months of pregnancy.
The endometrium (lining of the uterus) remains spongy and vascular to support the PLACENTA. A plug of mucus collects in the cervix, helping block BACTERIA from entering the uterus. The tissues of the VAGINA and VULVA engorge with blood, softening in preparation for childbirth. As the pregnancy approaches term, the cervix softens and thins (effaces). With the contractions of labor the cervix dilates and the vagina expands to allow passage of the fetus.
Changes in the breasts, notably tenderness and swelling, are often the earliest indications of pregnancy as the breasts respond to the hormones. As pregnancy progresses a woman’s breasts greatly enlarge and change in preparation for BREASTFEEDING (lactation) after birth. The mammary glands and ducts (milk glands and ducts) swell and around the seventh month begin producing colostrum, a fatty premilk that conveys important NUTRIENTS and antibodies for basic immunity to the infant.
A woman’s blood volume and cardiac output progressively increase as pregnancy advances. The heart enlarges somewhat, HEART RATE goes up, and blood pressure rises. In very early pregnancy the blood vessels dilate in anticipation of the increased blood volume, sometimes resulting in episodes of lightheadedness or dizziness. Some women also get vascular headaches in response to the changes taking place within the muscular walls of the arteries.
One of pregnancy’s early hallmarks is MORNING SICKNESS, nausea and vomiting doctors believe results from the hormones that surge into the woman’s blood circulation when the blastocyst implants. These same hormones are responsible for softening connective tissue and have similar actions on the muscular tissues of the gastrointestinal system, sometimes slowing peristalsis (movement of the intestines) enough to cause CONSTIPATION. Drinking plenty of fluids, eating foods high in fiber, and walking for at least 30 minutes every day help keep the gastrointestinal system functioning at its best.
In the later months of pregnancy the enlarged uterus displaces the organs of the upper abdomen further upward against the DIAPHRAGM, pressuring the stomach to cause DYSPEPSIA (upset stomach and heartburn) and gastric reflux. These discomforts go away after the baby is born and the abdominal organs return to their normal positions.
Weight gain is both normal and essential to support the pregnancy. Appropriate weight gain for a woman who is of healthy weight at the onset of pregnancy is 25 to 35 pounds; in OBESITY less weight gain, 15 to 25 pounds, is healthier for both mother and baby. About 15 to 18 pounds of the weight comes from the baby and organs that support it (uterus, placenta, AMNIOTIC FLUID). The changes in the breasts add 2 to 3 pounds; additional fluids (such as blood) and increased body fat account for the remainder. The most rapid weight gain typically occurs in the second trimester, 2 to 4 pounds per month.
Most women require only an additional 200 to 300 calories a day to meet their increased energy needs. Nutritious EATING HABITS are especially important to meet nutritional needs for vitamins and minerals. Pregnant women should take prenatal vitamins to make sure they receive adequate amounts of vital nutrients. Folic acid (folate) is particularly crucial for proper development of the BRAIN and SPINAL CORD. Supplemental iron boosts the ability of the woman’s blood to carry oxygen, helping prevent ANEMIA.
|THE WOMAN’S BODY THROUGH PREGNANCY – week by week pregnancy|
|Gestational Week||Body Characteristics|
|4 to 6||UTERUS soft and enlarged; breasts tender and swollen|
|12||belly begins to bulge; 2 to 4 pounds weight gain|
|16||darkened nipples and areola; dark line down center of abdomen|
|20||top of uterus at the level of the belly button; pregnancy obvious; breasts enlarged|
|24||Braxton-Hicks contractions; top of uterus above belly button; VULVA enlarged due to blood engorgement|
|28||weight gain of about 1 pound a week; minor swelling of the ankles and feet; size of uterus pressures BLADDER and DIAPHRAGM|
|32||breasts begin to leak colostrum; fetal movements visible through the abdominal wall|
|36||top of uterus near the bottom of the sternum; CERVIX begins to soften and thin (efface); pelvic ligaments and muscles soften and stretch|
|40||Strong Braxton-Hicks contractions; uterus completely fills the abdominal cavity; cervix continues to efface and begins to dilate; breasts engorged and frequently leak colostrum; mucous plug dislodges from cervix; water breaks (amniotic membrane ruptures)|
Health Care During Pregnancy
Though pregnancy is a natural event, not a medical condition, routine PRENATAL CARE provides optimal circumstances for the health of the woman and of the fetus. Current medical knowledge and technology make possible high-risk pregnancies as well as early intervention to avert or manage medical complications that may arise in the woman or the fetus. Screening tests and procedures can detect congenital and genetic abnormalities (BIRTH DEFECTS) that may require special medical attention during or after birth.
For further discussion of pregnancy within the context of the structures and functions of reproduction and sexuality, please see the overview section “The Reproductive System.”