Maternal exercise lowers fetal heart rate

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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.

4 Replies to “Maternal exercise lowers fetal heart rate”

  1. As a completely anecdotal aside, which may be of interest to active expectant mothers (or parents of chubby babies) I exercised heavily with my second child, routinely pushing my heartrate over the recommended 150 bpm. In utero, the baby became very active while I was at rest, kicking so hard on several occasions that I nearly fell over (perhaps trying to tell me something?!) He was born voracious, nursing so frequently and gaining so much weight in his first week as to break the nurse’s scale. He went on to become an exceedingly fat infant during the nursing phase — but the baby weight melted off as soon as he started to walk (and run).

  2. Thanks for the comment, Kiki! It would be interested to see if fetal activity (i.e. that powerful kick) is also correlated with maternal exercise.

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