Why is the supine position not recommended during the later stages of pregnancy?

The supine position is not recommended during the later stages of pregnancy primarily because of the potential risk of the fetus applying pressure on important blood vessels, specifically the inferior vena cava. When a pregnant person lies flat on their back, the weight of the uterus and the fetus can compress the inferior vena cava, which is responsible for returning blood from the lower body to the heart. This compression can lead to decreased blood flow not only back to the heart but also to the placenta, hence reducing the oxygen and nutrient supply to the developing fetus.

This condition, known as supine hypotensive syndrome, can lead to a range of issues such as dizziness, nausea, and even fetal distress if blood flow is significantly compromised. Therefore, alternative positions, such as side-lying or propping up with pillows, are encouraged to ensure both comfort and safety for both the pregnant individual and the fetus.