These issues happen as the tummy rests on the intestines and main blood vessels like the vana cava and aorta upon you sleep on the back. (vkool.com)
-- During pregnancy the baby may actually press on the main blood vessel that returns blood to the heart. (fullhealthsecrets.com)
By clogging the main blood vessels, the blood supply to other organs of the body is reduced, particularly the lungs, liver and kidneys, leading to malfunction of these organs. (chai-online.org)