During pregnancy, at what point should you start sleeping on your back? at some point in the pregnancy ive heard that you shouldnt sleep on your back? at what week, and why?

After : After about twenty weeks gestation, the uterus becomes large and heavy, and if you lie on your back, the heavy uterus can press against the large blood vessels- the aorta and the vena cava- that run behind the uterus. If these vessels get compressed, blood flow to the uterus may be compromised, and return of the blood from the lower extremities can be impeded. In order to maximize blood flow to the fetus and keep circulation open in the mother, it’s best to sleep on one side or the other (some say the left side is better, but don’t worry if you flip like a tuna from left to right in your sleep like i did when i was pregnant).