Although it was a small, preliminary study, researchers say the results build on previous research showing that women benefit from exercise during pregnancy.
"This study suggests that a mother who exercises may not only be imparting health benefits to her own heart, but to her developing baby's heart as well," researcher Linda May of the Kansas City University of Medicine and Biosciences (KCUMB) in Kansas City, Mo., says in a news release.
"As a result of this pilot study, we plan to continue the study to include more pregnant women."
Pregnancy and Exercise
In the study, presented this week at the Experimental Biology 2008 conference, researchers monitored fetal heart rate and variability in a group of 10 pregnant women every four weeks from 24 weeks gestation until full term.
Half of the women reported that they engaged in moderate-intensity aerobic exercise for at least 30 minutes a day, three times a week, and the other half did not exercise.
Six of the 10 women completed the study. The results showed that there were lower heart rates among fetuses of the three mothers who exercised during pregnancy. Fetal heart rates among non-exercisers were higher regardless of the fetal activity or gestational age.
These differences in fetal heart rates were statistically significant at each stage. Differences in long-term heart rate variability were also statistically significant at 32 weeks. The researchers plan to continue the study with more women to confirm their preliminary findings.
Researchers say the study suggests that exercise during pregnancy can have a beneficial effect on fetal cardiac programming by reducing fetal heart rate and increasing heart rate variability, essentially training the developing heart to work more efficiently.