Recommendations for exercise during pregnancy have undergone significant modifications since 1985. Initial guidelines placed restrictions on exercise intensity and duration, limiting women to a heart rate of less than 140 beats per minute and restricting exercise to 15 minutes or less. Following publication of numerous studies that showed maternal benefits from regular exercise during pregnancy and safety to the health of the baby, guidelines were relaxed in 1984. Although restrictions on heart rate and exercise duration were removed, these guidelines offered only cautious approval to women wanting to engage in exercise while pregnant.
In 2002, the most progressive guidelines to date were released. These guidelines recommend that in the absence of either medical or obstetrical complications, pregnant women who exercised before they were pregnant should participate in 30 minutes or more of moderately intense exercise on most, if not all, days of the week. Running, along with cross-training, such as swimming, stationary cycling, and cross-country skiing are now recommended and acceptable forms of exercise. Although upper limits on physical activity and intensity do not yet exist, the guidelines do give consideration to competitive athletes and their more strenuous training schedules as long as they remain under close obstetric supervision.
As the guidelines have evolved, acceptance by the medical profession is growing. It’s understandable, however, why the medical community has been slow to endorse exercise, and running in particular, during pregnancy. Research in this area is inherently difficult. There are ethical concerns about research involving pregnant women, and much of the data comes from research on animals. Human studies have been difficult to compare because of differences in study design; maternal fitness levels; varied exercise activities, intensities, and duration; and the time during the pregnancy the exercise is performed. Despite these difficulties, when everything is evaluated together, clear maternal benefits can be gained from running during your pregnancy.
Benefits of Exercise During Pregnancy
Frequent complaints of pregnancy, including nausea, heartburn, insomnia, varicose veins, and leg cramps are reduced in women who remain active during their pregnancy. Other common discomforts of pregnancy, including fatigue, back pain, swelling of the extremities, and shortness of breath are also lessened. Exercising while pregnant can greatly impact a woman’s cardiorespiratory fitness. A study of women runners who continued to run during their pregnancy improved their maximal aerobic capacity 8 to 10 percent more than that of a group of nonpregnant runners followed over the same period.
Exercise during pregnancy has also been associated with a reduced risk of developing certain obstetrical complications, including preeclampsia, pregnancy-induced hypertension, and gestational diabetes. (See table 3.1, page 38, for more information on these conditions.) However, a study in Dutch women published in 2009 calls into question the possibility that the risk of preeclampsia may be decreased. Women engaging in more than four and a half hours per week of physical exercise in the first trimester showed a significantly greater increase in the risk of developing severe preeclampsia than women participating in less physical activity. This suggests that an upper limit for exercise may exist during the first trimester. Future studies are needed to clarify these findings. While a relationship between exercise and length of labor has not been demonstrated, exercise during pregnancy has been associated with better tolerance of labor and a lower risk of Cesarean-section childbirth.
Circumstances That Prevent Training and Racing
Despite the liberalization of these guidelines, legitimate medical conditions that already exist or develop during pregnancy could prohibit you from running and racing while pregnant. Significant heart and lung disease, persistent bleeding in the second and third trimesters, and ruptured membranes are just some of these conditions. The table below, from Running for Women by Jason Karp, PhD and Carolyn Smith, MD, contains a complete list. Several other conditions require a careful evaluation of the risks and benefits before you continue your running program. The most common of these include severe anemia, being extremely underweight, poorly controlled thyroid disease, and inappropriate fetal size and development. Although these conditions will not necessarily prohibit you from running during your pregnancy, experiencing them will require close monitoring by your obstetric provider.
Circumstances can develop that mean you should stop exercising. You should be aware of how important it is to change your running regimen if changes in your pregnancy make this necessary, and you need to know the warning signals that require an evaluation by a physician. In pregnant women these warning signs include the following:
- Vaginal bleeding
- Breathlessness at rest or out of proportion to the effort
- Chest pain
- Racing heart
- Muscle weakness
- Significant swelling in feet or legs
- Uterine contractions that occur more than 30 minutes after exercise
- Decreased fetal movement
- Pelvic, hip, or worsening back pain
- Chronic fatigue
- Leakage of fluids
Many women continue running during pregnancy until it becomes too uncomfortable to do so. When this occurs, consider switching to nonweight-bearing exercises, such as pool running or swimming.