Regular exercise leads to improved fitness for pregnant women, just as it does for all women and men. It helps keep the heart, mind and entire body healthy. Exercise helps prevent health problems like heart disease, high blood pressure, diabetes, osteoporosis (bone loss), anxiety, depression and, possibly, some forms of cancer.

For the pregnant woman, exercise can ease many common discomforts of pregnancy, such as constipation, backache, fatigue, sleep disturbances and varicose veins. Regular exercise also may help prevent pregnancy-related forms of diabetes and high blood pressure (1, 2). Fit women may be able to cope better with labor and have a faster recovery after delivery.

Pregnant women who have not exercised regularly should consider gradually increasing their activities or starting a mild exercise program to reap some of these health benefits. However, all pregnant women should check with a health care provider before starting or continuing exercise. Most women will be able to maintain their exercise program throughout pregnancy, although some may need to modify their activities. 

Women who do not want to participate in a regular exercise program can obtain many of the health benefits of exercise by following an active lifestyle. Past recommendations stated that a person needed to exercise continuously for about 30 minutes at least three times a week to obtain health benefits. However, current recommendations from the Centers for Disease Control and Prevention (CDC) say that short bouts of activity (at least 10 minutes each) several times a day also are effective (3).  

Is exercise safe for all pregnant women?
No. Women who should not exercise while pregnant include those who have (1):

• Heart disease that compromises blood flow

• Restrictive lung disease

• Preterm labor in the current pregnancy

• Cervical insufficiency (also called incompetent cervix), a defect of the cervix that results in early pregnancy loss or premature delivery

• Multiple gestation (twins, triplets or more), which increases the risk for preterm labor
• Persistent vaginal bleeding in the second or third trimester
• Ruptured membranes (bag of waters)

• Preeclampsia, a pregnancy-related form of high blood pressure

• Placenta previa, a low-lying placenta that covers part or all of the opening of the cervix during the third trimester  

Women with a history of medical problems (such as severe anemia or poorly controlled high blood pressure, diabetes, thyroid disease or seizure disorder) should exercise only with the approval of their health care provider. Pregnant women who are obese or extremely underweight should seek medical approval before starting an exercise routine. 

Can exercise harm the baby?
There is no evidence that exercise has any harmful effects on the unborn baby, or that it increases the risk of miscarriage, premature labor or birth defects in a normal pregnancy.

In the past, there were few good studies on the effects of exercise on the baby. Providers had theoretical concerns that it could trigger premature labor because exercise increases the levels of hormones that may stimulate uterine contractions. Recent studies have provided reassurance that exercise does not increase the risk for premature labor in low-risk pregnancies (4, 5). 

Providers also were concerned that regular exercise could slow fetal growth because during exercise, blood tends to be diverted to the exercising muscles and, possibly, away from the uterus. Most studies have found that exercise has no effect on birthweight, and a few studies suggest that moderate exercise may actually increase birthweight (4, 5). Recent studies have found that moderate exercise in early pregnancy improves growth of the placenta (6). The placenta supplies the baby with oxygen and nutrients, possibly contributing to an increase in birthweight.

Studies suggest that strenuous exercise, when continued through the third trimester of pregnancy, may slightly reduce birthweight (4, 5). It does not, however, appear to increase a woman's risk for having a low-birthweight baby (less than 5½ pounds). Some studies found that women who exercised strenuously throughout pregnancy had babies who were, on average, about 8 ounces lighter than the babies of a group of fit women who stopped exercising during pregnancy (4, 5). However, the weight difference was mainly in body fat, and the babies remained in the normal range for weight.

A study that followed this group of babies through age 5 found that the children of exercisers continued to be somewhat leaner than the children of nonexercisers, although their growth was in the normal range (2). And, for reasons that are not clear, the children of the exercisers scored significantly higher than the other children in tests of intelligence and language skills.

Does pregnancy change how a woman's body responds to physical activity?
During pregnancy, a woman's body changes in a number of ways that alter her response to exercise. For example, a pregnant woman's tolerance for strenuous exercise decreases as pregnancy progresses. Pregnant women require more oxygen than non-pregnant women, even at rest. As pregnancy progresses, women have to work harder to breathe because the enlarging uterus crowds the diaphragm (the large muscle separating the chest and abdomen). These changes mean that there is less oxygen available for use during exercise, making it easier to become out of breath. 

The cardiovascular system also changes during pregnancy. It responds differently to certain body positions. If a woman in her second or third trimester exercises while lying flat on her back, her expanding uterus may compress the major vein (vena cava) that carries blood back to the heart from the legs. This causes her heart to beat more slowly. A slow heartbeat can cause dizziness and interfere with normal blood flow to the uterus. Similarly, motionless standing also causes the heart to beat more slowly. Therefore, pregnant women should avoid these positions.

Some studies suggest that a pregnant woman's body dissipates heat more efficiently. A pregnant woman starts sweating at a lower body temperature than a non-pregnant woman, so her temperature actually falls slightly during exercise (5). This adaptation may help protect the baby. Pregnant women should still take steps to avoid overheating, especially during the first trimester; during this time a sustained body temperature of 102.5° F or higher may increase the risk for certain birth defects of the brain and spine. However, studies have not shown any increase in these or other birth defects among babies of women who exercise vigorously during pregnancy (1, 5).

Pregnancy alters a woman's sense of balance. The enlarging uterus and breasts shift her center of gravity. High hormone levels make her connective tissues more lax, and her joints may be more susceptible to injury. All of these changes determine the types of exercises that are safest for pregnant women.

What are some guidelines for exercising safely during pregnancy?
According to ACOG, participation in a range of recreational programs appears safe for most pregnant women (1). However, a pregnant woman should always check with her health care provider to make sure she can safely continue her exercise program. These precautions can help assure that an exercise program is safe for mother and baby (1, 7):

• Avoid contact sports and any activities that can cause even mild trauma to the abdomen, such as ice hockey, kickboxing, soccer and basketball.

• Avoid activities with a high risk for falling, such as gymnastics, horseback riding, downhill skiing and vigorous racquet sports.

• Avoid scuba diving throughout pregnancy. This activity puts the baby at increased risk for decompression sickness and may contribute to miscarriage, birth defects, poor fetal growth and preterm labor.

• Avoid exercising on the back after the first trimester. Also avoid prolonged periods of motionless standing. Both can reduce blood flow to the uterus.

• Avoid jerky, bouncing or high-impact movements that may strain joints and cause injuries.

• Avoid exercising at high altitudes (more than 6,000 feet) because it can lead to reduced amounts of oxygen reaching the baby. 

• Eat an adequate diet to gain 25 to 35 pounds (or the amount of weight recommended by her health care provider) over the nine months. Most pregnant women require approximately 300 additional calories a day. Those who exercise regularly may require more.

• Avoid overheating, especially in the first trimester. Drink plenty of fluids before, during and after exercise. Wear layers of "breathable" clothing and do not exercise on hot, humid days. Avoid hot tubs, saunas and Jacuzzis.

What types of exercise are best during pregnancy?
Most pregnant women can continue their pre-pregnancy exercise programs, though they may need to modify some activities or decrease the intensity of workouts as pregnancy progresses. For example, a jogger who quickly becomes fatigued or breathless may switch to brisk walking.

Women who participated in a strength training program before pregnancy often can safely continue their training during pregnancy, as long as they do so in moderation. They should always check with their providers to see how much weight is safe for them to lift. They should probably avoid lifting while lying on their back.

If a pregnant woman is just starting an exercise program (with her health care provider's OK), walking, swimming, cycling on a stationary bicycle and aerobics (low impact or a class for pregnant women) are activities that usually are safe.   

A pregnant woman should stop exercising immediately and call her health care provider if she experiences symptoms such as (1):

• Vaginal bleeding

• Dizziness

• Increased shortness of breath

• Headache

• Chest pain

• Muscle weakness

• Calf pain or swelling

• Uterine contractions

• Leakage of amniotic fluid

• Decreased fetal movement

When can a woman begin postpartum exercises?
According to ACOG, some women can resume their exercise program within days of delivery, while others may need to wait longer (7). Many of the physical changes that occur during pregnancy take approximately four to six weeks before returning to their pre-pregnancy state. For that reason, women should gradually build up to their pre-pregnancy exercise routines following delivery. A woman should check with her health care provider to see what is right for her.

Women who exercise regularly during pregnancy build stamina and muscle tone. After delivery, this allows them to build up to their previous level of exercise more quickly than mothers who do not exercise regularly. New mothers who resume exercise (and moms who breastfeed) lose more weight than those who do not exercise, and most exercising mothers are back to their pre-pregnancy weight by their baby's first birthday.

A 1999 study showed that exercise has psychological payoffs for new mothers (8). Women who resumed their exercise program within six weeks of delivery felt better about themselves and adjusted more quickly to being a mom than women who did not exercise. While exercise benefits body and mind, women need to remember that pregnancy-related changes in bodily systems (such as the cardiovascular system) persist for about four to six weeks after giving birth. Therefore, a woman should start slowly. If she feels pain or has other unusual symptoms during a specific exercise, she should temporarily avoid that exercise (or do fewer repetitions or a shorter routine). A woman who has had a cesarean delivery should not exercise strenuously until her health care provider gives her the go-ahead.

References

1. American College of Obstetricians and Gynecologists (ACOG). Exercise During Pregnancy and the Postpartum Period. ACOG Committee Opinion, number 267, January 2002 (reaffirmed 2005).

2. American College of Sports Medicine. Roundtable Consensus Statement: Impact of Physical Activity During Pregnancy and Postpartum on Chronic Disease Risk. Medicine and Science in Sports and Exercise, 2006, pages 989-1005.

3. Centers for Disease Control and Prevention (CDC). Physical Activity for Everyone: Physical Activity Terms, last reviewed 3/22/06.

4. Clapp, J.F., III. Recommending Exercise During Pregnancy. Contemporary Ob/Gyn, January 2001, pages 30-49.

5. Morris, S.N. and Johnson, N.R. Exercise During Pregnancy: A Critical Appraisal of the Literature. Journal of Reproductive Medicine, volume 50, number 3, March 2005, pages 181-188.

6. Clapp, J.F. Influence of Endurance Exercise and Diet on Human Placental Development and Fetal Growth. Placenta, June-July 2006, volume 27, pages 527-534.

7. American College of Obstetricians and Gynecologists (ACOG). Exercise During Pregnancy. Educational pamphlet AP119. ACOG, Washington, D.C., June 2003.

8. Sampselle, C.M., et al. Physical Activity and Postpartum Well-Being. Journal of Obstetric, Gynecologic and Neonatal Nursing, January/February 1999, pages 41-49.

March 2007