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Physical Changes During Pregnancy

by Haywood L. Brown, MD

Pregnancy causes many changes in a woman’s body. Most of them disappear after delivery. These changes cause some symptoms, which are normal. However, certain disorders, such as gestational diabetes (see Gestational diabetes), can develop during pregnancy, and some symptoms may indicate such a disorder.

Symptoms that should be immediately reported to a doctor if they occur during pregnancy include the following:

  • Persistent or unusual headaches

  • Persistent nausea and vomiting

  • Light-headedness

  • Disturbances of eyesight

  • Pain or cramps in the lower abdomen

  • Contractions

  • Vaginal bleeding

  • Leakage of amniotic fluid (described as "the water breaks")

  • Swelling of the hands or feet

  • Decreased urine production

  • Any illness or infection

  • Tremor (shaking of the hands, feet, or both)

  • Seizures

  • Rapid heart rate

  • Decreased movement of the fetus

General health

Fatigue is common, especially in the first 12 weeks and again in late pregnancy. The woman may need to get more rest than usual.

Reproductive tract

By 12 weeks of pregnancy, the enlarging uterus may cause the woman’s abdomen to protrude slightly. The uterus continues to enlarge throughout pregnancy. The enlarging uterus extends to the level of the navel by 20 weeks and to the lower edge of the rib cage by 36 weeks.

The amount of normal vaginal discharge, which is clear or whitish, commonly increases. This increase is usually normal. However, if the discharge has an unusual color or smell or is accompanied by vaginal itching and burning, a woman should see her doctor. Such symptoms may indicate a vaginal infection. Some vaginal infections, such as trichomoniasis (a protozoan infection—see Trichomonas Vaginitis) and candidiasis (a yeast infection—see Vaginal Yeast Infection (Candidiasis)), are common during pregnancy and can be treated.

Breasts

The breasts tend to enlarge because hormones (mainly estrogen ) are preparing the breasts for milk production. The glands that produce milk gradually increase in number and become able to produce milk. The breasts may feel firm and tender. Wearing a bra that fits properly and provides support may help.

During the last weeks of pregnancy, the breasts may produce a thin, yellowish or milky discharge (colostrum). Colostrum is also produced during the first few days after delivery, before breast milk is produced. This fluid, which is rich in minerals and antibodies, is the breastfed baby's first food.

Heart and blood flow

During pregnancy, the woman’s heart must work harder because as the fetus grows, the heart must pump more blood to the uterus. By the end of pregnancy, the uterus is receiving one fifth of the woman’s prepregnancy blood supply. During pregnancy, the amount of blood pumped by the heart (cardiac output) increases by 30 to 50%. As cardiac output increases, the heart rate at rest speeds up from a normal prepregnancy rate of about 70 beats per minute to 80 or 90 beats per minute. During exercise, cardiac output and heart rate increase more when a woman is pregnant than when she is not. At about 30 weeks of pregnancy, cardiac output decreases slightly. Then during labor, it increases by an additional 30%. After delivery, cardiac output decreases rapidly at first, then more slowly. It returns to the prepregnancy level about 6 weeks after delivery.

Certain heart murmurs and irregularities in heart rhythm may appear because the heart is working harder. Sometimes a pregnant woman may feel these irregularities. Such changes are normal during pregnancy. However, other abnormal heart sounds and rhythms (for example, diastolic murmurs and a rapid, irregular heart rate), which occur more often in pregnant women, may require treatment.

Blood pressure usually decreases during the 2nd trimester but may return to a normal prepregnancy level in the 3rd trimester.

The volume of blood increases by almost 50% during pregnancy. The amount of fluid in the blood increases more than the number of red blood cells (which carry oxygen). Thus, even though there are more red blood cells, blood tests indicate mild anemia, which is normal. For reasons not clearly understood, the number of white blood cells (which fight infection) increases slightly during pregnancy and increases markedly during labor and the first few days after delivery.

Did You Know...

  • The volume of a woman's blood increases by 50% during pregnancy.

The enlarging uterus interferes with the return of blood from the legs and the pelvic area to the heart. As a result, swelling (edema) is common, especially in the legs. Varicose veins commonly develop in the legs and in the area around the vaginal opening (vulva). They sometimes cause discomfort. Clothing that is loose around the waist and legs is more comfortable and does not restrict blood flow. Some measures not only ease the discomfort but may also reduce leg swelling and make varicose veins more likely to disappear after delivery:

  • Wearing elastic support hose

  • Resting frequently with the legs elevated

  • Lying on the left side

Urinary tract

Like the heart, the kidneys work harder throughout pregnancy. They filter the increasing volume of blood. The volume of blood filtered by the kidneys reaches a maximum between 16 and 24 weeks and remains at the maximum until just before the baby is due. Then, pressure from the enlarging uterus may slightly decrease the blood supply to the kidneys.

Activity of the kidneys normally increases when a person lies down and decreases when a person stands. This difference is amplified during pregnancy—one reason a pregnant woman needs to urinate frequently while trying to sleep. Late in pregnancy, lying on the side, particularly the left side, increases kidney activity more than lying on the back. Lying on the left side relieves the pressure that the enlarged uterus puts on the main vein that carries blood from the legs. As a result, blood flow improves and kidney activity increases.

The uterus presses on the bladder, reducing its size so that it fills with urine more quickly than usual. This pressure also makes a pregnant woman need to urinate more often and more urgently.

Respiratory tract

The high level of progesterone , a hormone produced continuously during pregnancy, signals the brain to lower the level of carbon dioxide in the blood. As a result, a pregnant woman breathes slightly faster and more deeply to exhale more carbon dioxide and keep the carbon dioxide level low. She may breathe faster also because the enlarging uterus limits how much the lungs can expand when she breathes in. The circumference of the woman’s chest enlarges slightly.

Virtually every pregnant woman becomes somewhat more out of breath when she exerts herself, especially toward the end of pregnancy. During exercise, the breathing rate increases more when a woman is pregnant than when she is not.

Because more blood is being pumped, the lining of the airways receives more blood and swells somewhat, narrowing the airways. As a result, the nose occasionally feels stuffy, and the eustachian tubes (which connect the middle ear and back of the nose) may become blocked. These effects can slightly change the tone and quality of the woman’s voice.

Digestive tract

Nausea and vomiting, particularly in the mornings (morning sickness), are common. They may be caused by the high levels of estrogen and human chorionic gonadotropin, two hormones that help maintain the pregnancy. Nausea and vomiting may be relieved by changing the diet or patterns of eating. For example, drinking and eating small portions frequently, eating before getting hungry, and eating bland foods (such as bouillon, consommé, rice, and pasta) may help. Eating plain soda crackers and sipping a carbonated drink may relieve nausea. Keeping crackers by the bed and eating one or two before getting up may relieve morning sickness. No drugs specifically designed to treat morning sickness are currently available. If nausea and vomiting are so intense or persistent that dehydration, weight loss, or other problems develop, a woman may need to be treated with drugs that relieve nausea (antiemetic drugs) or to be hospitalized temporarily and given fluids intravenously (see Hyperemesis Gravidarum).

Heartburn and belching are common, possibly because food remains in the stomach longer and because the ringlike muscle (sphincter) at the lower end of the esophagus tends to relax, allowing the stomach’s contents to flow backward into the esophagus. Several measures can help relieve heartburn:

  • Eating smaller meals

  • Not bending or lying flat for several hours after eating

  • Avoiding caffeine, tobacco, alcohol, and aspirin and related drugs (salicylates)

  • Taking liquid antacids, but not antacids that contain sodium bicarbonate because they contain so much salt (sodium)

Heartburn during the night can be relieved by the following:

  • Not eating for several hours before going to bed

  • Raising the head of the bed or using pillows to raise the head and shoulders

The stomach produces less acid during pregnancy. Consequently, stomach ulcers rarely develop during pregnancy, and those that already exist often start to heal.

As pregnancy progresses, pressure from the enlarging uterus on the rectum and the lower part of the intestine may cause constipation. Constipation may be worsened because the high level of progesterone during pregnancy slows the automatic waves of muscular contractions in the intestine, which normally move food along. Eating a high-fiber diet, drinking plenty of fluids, and exercising regularly can help prevent constipation.

Hemorrhoids, a common problem, may result from pressure of the enlarging uterus or from constipation. Stool softeners, an anesthetic gel, or warm soaks can be used if hemorrhoids hurt.

Pica, a craving for strange foods or nonfoods (such as starch or clay), may develop.

Occasionally, pregnant women, usually those who also have morning sickness, have excess saliva. This symptom may be distressing but is harmless.

Skin

Mask of pregnancy (melasma) is a blotchy, brownish pigment that may appear on the skin of the forehead and cheeks. The skin surrounding the nipples (areolae) may also darken. A dark line commonly appears down the middle of the abdomen. These changes may occur because the placenta produces a hormone that stimulates melanocytes, the cells that make a dark brown skin pigment (melanin).

Pink stretch marks sometimes appear on the abdomen. This change probably results from rapid growth of the uterus and an increase in levels of adrenal hormones.

Small blood vessels may form a red spiderlike pattern on the skin, usually above the waist. These formations are called spider angiomas. Thin-walled, dilated capillaries may become visible, especially in the lower legs.

Two intensely itchy rashes occur only during pregnancy:

  • Pruritic urticarial papules and plaques of pregnancy (urticaria of pregnancy—see Pruritic Urticarial Papules and Plaques of Pregnancy) typically appears during the last 2 to 3 weeks of pregnancy but may appear any time after the 24th week. Its cause is unknown.

  • Herpes gestationis (see Pemphigoid Gestationis) can appear any time after the 12th week of pregnancy or immediately after delivery. The cause is thought to be abnormal antibodies that attack the body’s own tissues—an autoimmune reaction.

Hormones

Pregnancy affects virtually all hormones in the body, mostly because of the effects of hormones produced by the placenta. For example, the placenta produces a hormone that stimulates the woman’s thyroid gland to become more active and produce larger amounts of thyroid hormones. When the thyroid gland becomes more active, the heart may beat faster, causing the woman to become aware of her heartbeat (have palpitations). Perspiration may increase, mood swings may occur, and the thyroid gland may enlarge. However, the disorder hyperthyroidism, in which the thyroid gland malfunctions and is overactive, develops in fewer than 0.1% of pregnancies.

Levels of estrogen and progesterone increase early during pregnancy because human chorionic gonadotropin, the main hormone the placenta produces, stimulates the ovaries to continuously produce them. After 9 to 10 weeks of pregnancy, the placenta itself produces large amounts of estrogen and progesterone . Estrogen and progesterone help maintain the pregnancy.

The placenta stimulates the adrenal glands to produce more aldosterone and cortisol (which help regulate how much fluid the kidneys excrete). As a result, more fluids are retained.

During pregnancy, changes in hormone levels affect how the body handles sugar. Early in pregnancy, the sugar (glucose) level in the blood may decrease slightly. But in the last half of pregnancy, the level may increase. More insulin (a hormone that controls the sugar level in the blood) is needed during pregnancy. Consequently, diabetes, if already present, may worsen during pregnancy. Diabetes can also begin during pregnancy. This disorder is called gestational diabetes (see Gestational diabetes).

Joints and muscles

The joints and ligaments (fibrous cords and cartilage that connect bones) in the woman’s pelvis loosen and become more flexible. This change helps make room for the enlarging uterus and prepare the woman for delivery of the baby. As a result, the woman’s posture changes somewhat.

Backache in varying degrees is common because the spine curves more to balance the weight of the enlarging uterus. Avoiding heavy lifting, bending the knees (not the waist) to pick things up, and maintaining good posture can help. Wearing flat shoes with good support or a lightweight maternity girdle may reduce strain on the back.

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