Exercise during pregnancy has a positive effect on moms' cardiovascular activity and also on their developing offspring, according to a new study.

In the study, which was led by Linda E. May of the Department of Anatomy, Kansas City University of Medicine and Biosciences (KCUMB), Kansas City, fetal recordings were obtained from 24 weeks to term.

The researchers hypothesized that maternal exercise during pregnancy can have a beneficial effect on fetal cardiac programming by reducing fetal heart rate and increasing heart rate variability. As a result, a key component of the research involved magnetocardiography (MCG), the magnetic correlate of an electrocardiogram (ECG).

MCG is a safe, non-invasive method to record the magnetic field surrounding the electrical currents generated by the fetal heart and nervous system.

In addition to measures of heart rate and variability, the MCG allows for the study of the cardiac waveforms to measure of cardiac time intervals.

Maternal and fetal events were recorded in real time. Fetal movements such as breathing, body and mouth movements were recorded using the MCG in order to determine fetal state and to track heart rate accelerations. The recordings were done at four-week intervals. The data were derived from fetal MCG conducted in the second and third trimesters of pregnancy and in the postnatal period. The data captured was used to measure fetal heart rate (HR) as derived from the fetal MCG recordings.

Ten women participated in the study. Each was classified as either an exerciser (n=5) or control (n=5). The women were grouped according to the frequency, intensity, and length of physical activity they engaged in.

The researchers found that the there were significantly lower heart rates among fetuses that had been exposed to maternal exercise. The heart rates among non-exposed fetuses were higher, regardless of the fetal activity or the gestational age.

At each stage of gestation the differences between the fetal heart rates of the two groups were statistically significant. The analysis of short- and long-term heart variability at 28, 32 and 36 weeks of gestation in exercise-exposed vs. non-exercise-exposed fetuses were statistically different at 32 wks. This trend is still seen at 36 wks, however it is not significant.

According to Dr. May, "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. As a result of this pilot study, we plan to continue the study to include more pregnant women."

The study 'Effects of Maternal Exercise on the Fetal Heart' will be presented at the 121st annual meeting of the American Physiological Society.