Pregnant women who exercise on a regular basis are not putting themselves or their baby in harm's way, a new study finds.
Researchers found that a mother's exercise lowered her baby's resting heart rate, a sign of good health for the baby's heart.
The study is one of the few that looked at the direct effect of exercise on the fetus. Researchers measured fetal heart beat and blood flow through the umbilical cord.
The results also showed that moms to-be who performed 30 minutes of exercise at a moderate or vigorous pace had lower heart rates than moms who exercised a little or not at all.
The findings support existing recommendations that most pregnant women begin or maintain an exercise program, getting at least 150 minutes of moderate aerobic exercise per week. However, the researchers noted that study findings did not apply to strenuous exercise. Moreover, only healthy pregnant women were involved in the study, not women who had pregnancy complications.
Researchers from Johns Hopkins University School of Medicine looked at 45 healthy pregnant women between 28 and 32 weeks of pregnancy, 15 who didn’t exercise, 15 who exercised regularly and 15 who exercised vigorously.
Women were split into two exercise groups, those who were highly active, exercising vigorously more than four days a week, and those who were regularly active, exercising moderately for 20 minutes three or more days a week.
The women first underwent treadmill tests to establish their baseline heart rate ranges for moderate and vigorous exercise sessions. They later returned to perform 30 minutes of exercise on a treadmill, by either walking or jogging.
After exercising, the heart rates of both the moms and babies were checked. Researchers found differences between the women, with the most highly active women having the lowest resting heart rate.
With moderate exercise, all baby health readings were similar before and after exercise. But with vigorous exercise, baby readings showed a decrease in blood flow resistance, which authors speculated could indicate improved blood circulation between mom and baby.
The researchers noted that they only looked at baby responses after one exercise session between 28 and 32 weeks of pregnancy, and said responses could be different during other stages of pregnancy.
According to current guidelines, participating in vigorous exercise during pregnancy is not recommended for women who aren't active, or in women who tend to exercise moderately. Women who are highly active may continue to workout at this level during pregnancy.
The study is published in the March issue of the journal Obstetrics and Gynecology.
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