Low-impact exercise during pregnancy--a study of safety

Exercise is an important part of many women's lives. Women are often advised to refrain from physical exercise during pregnancy. The reason given is mainly safety, i.e. fear of maternal hyperthermia, which is known to be related to neural tube defects. However, exercise during pregnancy has not been shown to be related to hyperthermia.

To study temperature and oxygen saturation responses to low-impact exercise in healthy pregnant women.

Forty pregnant women and 11 controls participating in low-impact aerobic exercise were monitored before exercise, at maximum-exercise level, and after exercise with regard to core temperature, heart rate, and oxygen saturation level.

The core temperature among the pregnant women did not increase significantly at maximum exercise or after exercise (36.5 versus 36.7 or 36.5 degrees C, P = 0.1, P = 0.5). None of the pregnant women were even close to approaching a dangerous body temperature at an intensity level of 69% of their maximum heart rate. As compared with pre-exercise values, oxygen saturation among pregnant women was significantly reduced at both maximum-exercise and postexercise measurements, but no measurement was below 95% in oxygen saturation.

Low-impact aerobics at about 70% of one's maximum heart rate appears to be safe in terms of risk of maternal hyperthermia.