Family Matters

When Mom Exercises in Pregnancy, Her Baby’s Heart Benefits

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One of the great things about pregnancy is that it offers a seemingly plausible excuse to indulge — eat a little more dessert (why not, when you’re going to gain so much weight anyway) and dial down that hard-core exercise regimen (see first parenthetical). But new research upends that mindset, showing that exercise during pregnancy can actually result in a healthier baby.

That exercising while pregnant is good for mom is hardly news, but now that mothers-to-be know it’s good for their babies, it will be that much harder to morph into a couch potato. Maternal guilt can now rear its head months before baby even appears on the scene, prompting Mom to hit the treadmill, hard. (More on Why Having Kids Is Bad for Your Health)

Previous research has indicated that exercise in the first trimester, when the placenta is formed, helps forge extra blood vessels so that there is more opportunity to exchange nutrients between mom and baby.

Linda May, an exercise physiologist and anatomist at Kansas City University of Medicine and Biosciences, figured there were bound to be sustained benefits for the baby too.

May and colleagues collected noninvasive fetal heart measurements from 66 fetuses when their mothers reached 28, 32 and 36 weeks of a typical 40-week pregnancy. Some of the mothers engaged in moderate to vigorous aerobic activity for 30 minutes at least three times a week; others didn’t exercise. (More on Time.comPregnant Women Awash in Chemicals. Is That Bad for Baby?)

Researchers then assessed fetal heart rate and heart rate variability, which is the span between beats. Heart rate variability is indicative of heart health, which is associated with better overall health: people with increased variability are exercisers, and their hearts function more efficiently; those with decreased variability may be cardiac patients or, at the least, couch potatoes.

At 32 weeks, researchers started to see changes in heart response in the fetuses of the exercising moms. By 36 weeks, they noted what May calls a “big, significant change” — lower heart rate and increased heart rate variability.

When researchers analyzed the frequency with which Mom exercised, they found that the more activity, the lower the fetal heart rate and the higher the heart rate variability. “If she just does a little bit, it will have benefit,” says May. “If she does more, it will help more. It’s similar to the exercise response of an adult. It’s very cool.” (More on Time.comWant Your Kids to Eat Healthier? It Starts with Mom)

Even cooler is the way the results continued to manifest themselves after birth. Some women dropped out of the research due to attrition, but 43 moms brought their babies back when they were 1 month old. Their hearts still showed that pumped-up quality, according to the study, which is slated for publication in the journal Early Human Development.

“It suggests the result we saw was real, and that it is giving this baby a healthier heart,” says May.

Forget onesies or an engraved Tiffany rattle; heart health sounds like a pretty good gift.