When pregnant athletes do weight training, their blood flow to the placenta temporarily goes up a little bit — and that’s a good thing because it means the baby isn’t getting less blood than it needs.

When pregnant women who regularly work out lift light to moderate weights (up to 50 lbs), their baby’s blood flow doesn’t drop—it actually goes up a little bit during the lift, which means it’s probably safe for them to do these exercises without worrying about cutting off the baby’s blood supply.

Pregnant women who regularly work out and do strength training may see better blood flow to the placenta during their workouts compared to other pregnant women, which could help the baby get more oxygen and nutrients.

Lifting weights up to 50 pounds while pregnant doesn't hurt blood flow to the baby—and might even help it a little—so the idea that lifting is always dangerous for the baby might not be true.

A special ultrasound technique can pick up tiny changes in blood flow to the placenta when a pregnant woman does strength training, which might help doctors watch over the baby's blood supply during workouts.