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.

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.

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.

When doctors press harder with the ultrasound wand on a pregnant person’s belly, it changes how blood flows in the baby’s brain—some speeds go up, one goes down, and one stays the same. It’s like squeezing a hose: the water flow changes, even if the baby is healthy.

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.