For most pregnant women, exercise is the last thing on their minds. After all, keeping slim while you’re expecting isn’t exactly the top priority — rather, it’s making sure your baby gets enough nutrients to grow. But in a small new study, researchers at the University of Auckland in New Zealand report that a mother’s regular aerobic exercise may be good for a growing fetus’ health — and may even help a baby get a healthier start in life.

The finding is a bit surprising, because exercise is known to lower the risk of insulin resistance — the precursor condition to diabetes. Although insulin resistance is a detriment in healthy adults, it turns out to be helpful for proper fetal development. Insulin-resistant individuals gradually lose their ability to respond to changing glucose levels in the blood; in pregnant women, the condition, which occurs when hormones produced by the placenta interfere with the proper function of insulin in the body, means nutrients get shunted to the growing baby. (If the condition gets severe, however, it can result in a temporary condition called gestational diabetes in the mother, which is associated with heavier babies and a higher risk of obesity in childhood.)

It’s an even more important message for overweight and obese mothers-to-be, who tend to deliver heavier babies (anything over about 8 lb. 12 oz., or 4 kg, is considered a high birth weight), who are then at higher risk of diabetes and obesity later in life. Those heavier children are then more likely to become overweight adults and in turn give birth to bigger babies. The goal, says Hofman, is to break the cycle of ever bigger generations of babies. According to his latest findings, exercise during pregnancy may be a safe and reliable first step; the American Congress of Obstetricians and Gynecologists recommends 30 minutes a day for pregnant women, for as long as they are physically able.