Physical Changes During Pregnancy

ByJessian L. Muñoz, MD, PhD, MPH, Baylor College of Medicine
Reviewed/Revised Sept 2024
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    Pregnancy causes many changes in a woman’s body. Many of the changes are temporary and return to a prepregnancy state within days or weeks after delivery (such as the heart beating faster with exercise, which is normal). However, women who develop a health issue or complication during pregnancy may have symptoms that are not normal changes from pregnancy.

    Symptoms that should be immediately reported to a doctor if they occur during pregnancy include the following (see also Symptoms During Pregnancy):

    • Nausea and vomiting that begin after the first trimester (or severe nausea and vomiting, even in the first trimester)

    • Vaginal bleeding or spotting

    • Pain or cramps in the lower abdomen

    • Fever, diarrhea, or other signs of infection

    • Vaginal discharge that is foul-smelling, itchy, yellow or green, or blood-tinged

    • Pain while urinating or needing to urinate much more frequently or urgently

    • Vaginal leakage of fluid (if the fluid does not seem like urine)

    • Swelling of feet or legs (especially if one leg is more swollen than the other) or of the hands or face

    • Rapid heart rate or chest pain

    • Shortness of breath

    • Light-headedness

    • Severe, persistent, or unusual headaches

    • Disturbances of eyesight

    • Decreased urine production

    • Seizures

    • Decreased movement of the fetus

    • Contractions

    If labor was quick in previous pregnancies, women should notify their doctor as soon as they have any indication that labor is starting.

    General health

    Fatigue is common, especially in the first 14 weeks and again in late pregnancy. Pregnant women may need to get more rest than usual.

    Reproductive tract

    By 12 weeks of pregnancy, the enlarging uterus may cause a 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, usually increases. If the discharge has an unusual color or smell or is accompanied by vaginal itching, a woman should see her doctor. Such symptoms may indicate a vaginal infection. Vaginal candidiasis (a yeast infection) is 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 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 a breastfed baby's first food. Nipple discharge that is blood-tinged is not normal and should be reported to a doctor.

    Heart and blood flow

    During pregnancy, a 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 a 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 as high as 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. Such changes are normal during pregnancy. Sometimes a pregnant woman may feel these irregularities, and she should discuss this with her doctor to see if testing for heart disorders is needed. Some abnormal heart sounds and rhythms require treatment.

    Blood pressure usually decreases during the second trimester and returns to a normal prepregnancy level in the third 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 almost 50% during pregnancy.

    The enlarging uterus puts pressure on the veins in the pelvic area and can slow down the return of blood from the legs and pelvic area to the heart. As a result, swelling (edema) of the feet and ankles is common. However, severe swelling of the feet or swelling of the calves or thighs or of the hands or face should be reported to a doctor immediately.

    Varicose veins commonly develop in the legs and in the area around the vaginal opening (vulva). They sometimes cause discomfort.

    The following measures not only ease 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

    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.

    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, which is one reason a pregnant woman may wake to urinate during the night. In the third trimester, 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. In addition, it puts pressure on the ureters (tubes that carry urine from the kidneys to the bladder). This pressure increases the risk of kidney infection (pyelonephritis), which can be dangerous in a pregnant woman.

    Respiratory tract

    The high level of progesterone, a hormone produced continuously during pregnancy, signals the body to breathe faster and deeper. As a result, a pregnant woman exhales more carbon dioxide to keep the level of carbon dioxide low. (Carbon dioxide is a waste product given off during respiration.) A woman may also breathe faster because the enlarging uterus puts pressure on the diaphragm (below the ribs) and limits how much the lungs can expand when she breathes in. The circumference of a woman’s chest enlarges slightly.

    Most pregnant women becomes somewhat more out of breath when they exert themselves, 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 voice.

    Digestive tract

    Nausea and vomiting, particularly in the mornings (morning sickness), are common in the first trimester and sometimes continue into the second and even third trimester. These symptoms may be caused by the high levels of estrogen and human chorionic gonadotropin, 2 hormones that help maintain the pregnancy.

    Nausea and vomiting may be relieved by changing the diet or pattern of eating—for example, by doing the following:

    • Drinking and eating small portions frequently

    • Eating bland foods (such as clear soup, rice, and plain crackers)

    • Sipping a carbonated drink

    • Keeping crackers by the bed and eating 1 or 2 before getting up

    Sometimes nausea and vomiting are so intense or persistent that dehydration, weight loss, or other problems develop—a disorder called hyperemesis gravidarum. Women with this disorder may need to be treated with medications that relieve nausea or to be hospitalized temporarily and given fluids intravenously.

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

    Heartburn and belching are common, possibly because food stays in the stomach longer. The digestive system moves more slowly due to the effect of progesterone and pressure from the enlarging uterus. Also, 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

    • Staying upright (not bending or lying down) for several hours after eating

    • Avoiding caffeine

    • Taking antacids (women should check with a doctor before taking any medications)

    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

    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, witch hazel, topical hemorrhoid medications (usually containing medications that shrink blood vessels, decrease inflammation, and/or reduce pain), or warm soaks can be used if hemorrhoids hurt.

    Pica, a craving for strange foods or nonfoods (such as starch or clay), develops in some pregnant women.

    Gallstones are more common during pregnancy.

    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 (called linea nigra) 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).

    Melasma
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    In some pregnant women, a blotchy, brownish pigment (melasma, or mask of pregnancy) appears on the skin of the forehead and cheeks (as shown in this photo).
    DR P. MARAZZI/SCIENCE PHOTO LIBRARY
    Linea Nigra
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    During pregnancy, a dark line (called linea nigra) may appear down the midabdomen.
    © Springer Science+Business Media

    Dark, pink, or white/silver 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.

    Spider Angiomas
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    Spider angiomas are small, bright-red spots that are surrounded by tiny blood vessels (capillaries), which resemble spider legs. They are normal in many healthy people. They commonly develop in women who are pregnant or use oral contraceptives and in people who have cirrhosis of the liver.
    Image provided by Thomas Habif, MD.

    Some skin conditions occur only during pregnancy, including the following intensely itchy rashes:

    • Polymorphic eruption of pregnancy typically appears during the last 2 to 3 weeks of pregnancy but may appear any time after the 24th week. Occasionally, they appear after delivery. The cause is unknown.

    • Pemphigoid (herpes) 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

    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.

    Pregnancy affects many hormones in the body, mostly because of the effects of hormones produced by the placenta. For example, the placenta produces a hormone that stimulates a 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 a woman to become aware of her heartbeat (have palpitations). However, it is rare to develop hyperthyroidism (overactivity of the thyroid gland) during 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. Later during pregnancy, the body does not respond as well to insulin (a hormone that controls the sugar [glucose] level in the blood) as it normally does. Consequently, the blood glucose level increases. The body needs to produce more insulin during pregnancy. Diabetes, if already present, may worsen during pregnancy. Diabetes can also begin during pregnancy. This disorder is called gestational diabetes.

    Joints and muscles

    The joints and ligaments (fibrous cords and cartilage that connect bones) in the pelvis loosen and become more flexible. This change helps make room for the enlarging uterus and prepares a woman's body for delivery of the baby.

    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 supportive band may reduce strain on the back.

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