It’s a common pregnancy myth that sleeping on your back hurts the baby, but in reality, it’s more uncomfortable for you than it is dangerous. Still, that doesn’t mean it is the most optimal sleep position, particularly as your pregnancy progresses.
Doctors typically recommend pregnant women stop sleeping on their stomachs and backs at around 20 weeks – the middle of the second trimester. Sleeping on your back is fine in the first trimester since your uterus isn’t large enough to cause any discomfort. But as your uterus gets heavier and your belly grows larger, you’ll be more comfortable sleeping on your side.
In the late second and third trimesters, sleeping on your back causes your heavy uterus to press on the inferior vena cava, which is the large vein that returns blood from your legs and lower half of the body to your heart. This compression decreases the amount of blood that returns to your heart. Your blood pressure may drop and you may begin to feel lightheaded, anxious and nauseated. If your blood pressure drops, this can potentially cause harm to your unborn child. Low blood pressure can decrease blood flow and nutrients to your uterus and developing infant.