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Maternal exercise lowers fetal heart rate

January 7th, 2012

A new study in Medicine & Science in Sports & Exercise, from the same group in Kansas City that previously found lower fetal heart rates when mothers exercised during pregnancy. This time, they were looking for a dose-response effect — the more exercise, the lower the heart rate — which would strengthen the case for causality rather than correlation. Here’s what they found:

“A” is “active” and “Q” is “quiet (as in whether the fetus is moving around or lying still). The Q results weren’t statistically significant, but for the A results, greater intensity did indeed lead to lower heart rates. But perhaps most significant is what they didn’t find:

Interestingly, maternal factors (i.e. maternal age, maternal resting HR, maternal weight gain, pre-pregnant BMI) did not influence the associations between physical activity and fetal parameters. Fetal cardiac autonomic control was enhanced in mothers who participated in physical activity regardless of the amount of weight they gained, their weight status prior to pregnancy, resting HR or age.

In other words, they’re not saying that fit mothers have fit babies; they’re saying that active mothers have fit babies.