Exercise is good for pregnant women. The U.S. Department of Health and Human Services (HHS) recommends that healthy pregnant women get at least 2½ hours of moderate-intensity aerobic activity a week (1). It’s best to spread this exercise throughout the week (1). This means that pregnant women should try to do 30 minutes of an aerobic activity on most, if not all days.
Regular physical activity leads to improved fitness for pregnant women. It helps keep the heart, mind and entire body healthy. It 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, 3). Fit women may be able to cope better with labor and recover faster after birth.
Pregnant women who have not been physically active should consider gradually increasing their activities or starting a mild exercise program to gain some of these health benefits. However, all pregnant women should check with their health care provider before starting or continuing exercise.
Women who do not want to participate in a traditional exercise program can get many of the health benefits of exercise by doing something physically active, like going for a walk. 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 HHS recommendations say that short bouts of physical activity (at least 10 minutes each) spread throughout the week are effective (1).
Are there any pregnant women who should not exercise?
Exercise is good for pregnant women, except in certain circumstances. Women should not exercise while pregnant if they have (2):
- Heart disease that compromises blood flow
- Preterm labor
- Incompetent cervix, a defect of the cervix that can cause pregnancy loss or premature birth
- Restrictive lung disease
- 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 also should seek medical approval before starting an exercise routine.
Can exercise harm the baby?
There is no evidence that moderate exercise has any harmful effects on an unborn baby, or that it increases the risk of miscarriage, preterm labor or birth defects in a normal pregnancy.
In the past, providers had concerns that exercise could trigger preterm labor because it increases the levels of hormones that may stimulate uterine contractions. Recent studies have shown that moderate exercise does not increase the risk for preterm labor in low-risk pregnancies (1, 4, 5). In fact, a 2008 Danish study suggests that moderate-to-heavy leisure-time physical activity (including sports, walking and gardening) may significantly reduce the risk of premature birth (6).
Some providers also were concerned that regular exercise could slow fetal growth. Most studies have found that moderate exercise has no effect on birthweight, and a few studies suggest that moderate exercise may actually increase birthweight (4, 5). Recent studies have shown that moderate exercise in early pregnancy improves growth of the placenta (6), possibly contributing to an increase in birthweight.
Few studies are available on the effects of strenuous exercise during pregnancy. Some studies suggest that women who continue to exercise strenuously through the third trimester of pregnancy may have babies with slightly reduced birthweight (4, 5, 8). Strenuous exercise does not, however, appear to increase a woman’s risk for having a low-birthweight baby (less than 5½ pounds).
One study that followed a group of babies through age 5 found that the children of women who exercised strenuously throughout pregnancy were somewhat leaner than the children of non-exercisers, although their growth was in the normal range (3). And, for reasons that are not clear, the children of the exercisers scored significantly higher than the children of non-exercisers in tests of intelligence and language skills (3).
Does pregnancy change how a woman’s body responds to physical activity?
Yes. During pregnancy, a woman’s body changes in a number of ways that alter her response to physical activity:
- Breathing: 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 physical activity, making it easier to become out of breath.
- Heart rate: A pregnant woman’s heart works harder and beats quicker to supply oxygen to the baby. As a result, she may have less energy for physical activity. Her cardiovascular system also 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 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. Motionless standing also causes the heart to beat more slowly.
- Body temperature: Some studies suggest that a pregnant woman’s body dissipates heat more efficiently than a non-pregnant woman’s body. 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 avoid overheating, especially during the first trimester, because 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 (2, 5).
- Balance: Pregnancy alters a woman’s sense of balance. The enlarging uterus and breasts shift her center of gravity.
- Joints: High hormone levels make a pregnant woman’s connective tissues more lax, and her joints may be more susceptible to injury.
What are some guidelines for exercising safely during pregnancy?
A pregnant woman should check with her health care provider to make sure the activities she chooses are safe during pregnancy. The following precautions can help assure that an exercise program is safe for mother and baby (2, 9). A pregnant woman should:
- 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 racquet sports.
- Avoid scuba diving. 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 her back after the first trimester. She also should avoid prolonged periods of motionless standing.
- 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.
- Avoid overheating, especially in the first trimester. She should drink plenty of fluids before, during and after exercise; wear layers of breathable clothing; not exercise on hot, humid days; and avoid hot tubs, saunas and steamrooms.
A pregnant woman should stop exercising immediately and call her health care provider if she experiences symptoms such as (2):
- 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
What types of physical activities are best during pregnancy?
Most pregnant women can continue their prepregnancy exercise programs, though they may need to modify some activities or decrease the intensity of workouts as pregnancy progresses. Women who participated in strength-training programs before pregnancy often can safely continue their training during pregnancy, as long as they do so in moderation. They should check with their provider to see how much weight is safe for them to lift and 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, aerobics (low impact or a class for pregnant women) and yoga classes for pregnant women are activities that usually are safe.
When can a woman begin postpartum exercises?
Some women can resume their exercise program within days of delivery, while others may need to wait longer (9). 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, these allow 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. Most exercising mothers are back to their prepregnancy weight by their baby’s first birthday.
Studies show that moderate exercise improves the mood of new mothers (1). A 1999 study shows that women who resume their exercise program within 6 weeks of delivery feel better about themselves and adjust more quickly to being a mom than women who do not exercise (10).
Pregnancy-related changes in bodily systems last for about 4 to 6 weeks after giving birth. Therefore, a woman should start or resume exercise slowly. If she feels pain or has other unusual symptoms during a specific activity, she should stop that activity (or do fewer repetitions or a shorter routine). A woman who has had a cesarean birth should not exercise strenuously until her health care provider gives her the go-ahead.
References
- U.S. Department of Health and Human Services (HHS). 2008 Physical Activity Guidelines for Americans. Washington, D.C., October 7, 2008.
- American College of Obstetricians and Gynecologists (ACOG). Exercise During Pregnancy and the Postpartum Period. ACOG Committee Opinion, number 267, January 2002 (reaffirmed 2005).
- 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.
- Clapp, J.F., III. Recommending Exercise during Pregnancy. Contemporary Ob/Gyn, January 2001, pages 30-49.
- 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.
- Hegaard, H.K., et al. Leisure Time Physical Activity Is Associated with Reduced Risk of Preterm Delivery. American Journal of Obstetrics and Gynecology, volume 198: 180.e1-e5.
- 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.
- Perkins, C.D., et al. Physical Activity and Fetal Growth During Pregnancy. Obstetrics and Gynecology, volume 109, number 1, January 2007, pages 81-87.
- American College of Obstetricians and Gynecologists (ACOG). Exercise During Pregnancy. Educational pamphlet AP119. ACOG, Washington, D.C., June 2003.
- Sampselle, C.M., et al. Physical Activity and Postpartum Well-Being. Journal of Obstetric, Gynecologic and Neonatal Nursing, January/February 1999, pages 41-49.
December 2008
