Placenta Under Normal Uterine Contraction and Compression of Vessels - Medical Illustration, Human Anatomy Drawing
This illustration shows that during a contraction the pressure inside the uterus and uterine wall is greater than the arterial pressure in the uterine artery, so there is no new blood flow into the uterus during a contraction. The same thing happens with the coronary arteries when the heart muscle contracts. Under normal circumstances, the baby tolerates this just fine.