why can't you lay on your back while pregnant

It is generally advised that pregnant people avoid lying on their back after about 20 weeks of pregnancy because the growing uterus can put pressure on major blood vessels, specifically the inferior vena cava and the aorta. This pressure can reduce blood flow back to the heart and to the fetus, potentially leading to low blood pressure, dizziness, nausea, fainting, decreased oxygen and nutrient delivery to the fetus, and other complications such as reduced fetal growth or even increased risk of stillbirth. Additionally, lying on the back can cause more back pain and increase the risk of sleep apnea during pregnancy. Side sleeping, particularly on the left side, is recommended as it promotes better circulation and reduces strain on key organs and blood vessels. If someone happens to wake up lying on their back, it is usually not a cause for immediate concern, as the body tends to adjust quickly for comfort and safety.