How Third-Trimester Exercise Benefits Your Baby

Exercise during pregnancy can keep weight gain in check, reduce your risk of gestational diabetes, decrease discomfort, and set you up for an easier labor and delivery. Now, new research shows that breaking a sweat, especially after 29 weeks, has a big benefit for your baby, too.

"The way I look at it, anything you're doing for you, you're doing for the baby, too," says Rebecca Scritchfield, a Washington, D.C.-based registered dietitian and ACSM certified health fitness specialist. Here's exactly how third trimester exercise benefits your little one.

Less Body Fat

In a study of 826 mothers and their babies, researchers found that mamas who exercised in their third trimesters gave birth to babies with less body fat, reports the journal Obstetrics & Gynecology. In fact, women who burned the most calories through third-trimester exercise gave birth to babies with 41.1 g less fat mass compared to women who exercised the least.

"Prenatal exercise may reduce the amount of glucose and fats mothers make available to their babies, helping them grow more optimally," says Dana Dabelea, MD, PhD, associate professor at the University of Colorado School of Public Health, and author of the study. Some experts also believe that babies born at healthy weights are also less likely to be obese in later life.

Even if you weren't active earlier in your pregnancy (thanks, morning sickness), it's never too late to start moving. The third trimester is when most of your baby's fat tissues develop, so that's when exercise may have the biggest payoff in terms of your baby's body fat, says Dr. Dabelea.

Better Heart Health

In a 2011 study from the Kansas City University of Medicine and Biosciences in Missouri, researchers assessed the heart activity of pregnant mothers and their infants-to-be. They found evidence that aerobic activity affects babies in much the same way that it helps their moms.

The women in this study had different levels of physical activity, but scientists found that the fetuses of pregnant women who worked out at least 30 minutes a day, three days a week, had lower heart rates (a sign of heart health). And when those women's one-month-old babies were tested, they also had lower heart rates, as well as better heart rate variability, which is a sign that their nervous systems were better controlling their hearts.

"If this result – that exercise offers cardiovascular protection – is supported by further research, it could certainly support the idea that healthy cardiovascular activity during pregnancy could be the best start for your baby's health in the future," says Sheryl Ross, M.D., an Ob-Gyn at Providence Saint John's Health Center in Santa Monica, California.

More Advanced Brains

A 2013 study published by researchers at the University of Montreal compared the cognitive development of two groups of babies. One half was born to moms who had at least 20 minutes of moderate-intensity cardiovascular exercise (think: walking or jogging) three days each week; the other, to moms who were sedentary. The researchers compared how the brains of both sets of babies responded to sound at one month of age, which is a measure of cognitive development. They found that babies born to the exercising mothers had more mature brain function – more advanced brains – than those born to the less active moms.

No one is sure yet how long that brain development advantage lasts – they're continuing to study it – but "these are very interesting results," says Dr. Ross. Whatever the ongoing research finds, even a little boost in brainpower sounds good to us.