One of the best things you can do for your baby is also one of the simplest: When sneaking in a midday nap or settling down for the night, lie on your left side. Doing so will help ensure that the baby receives optimal amounts of blood - a fetus' main source of essential nutrients, especially oxygen.

What's so right about the left? The two major blood vessels - the aorta (which delivers blood from the heart to the organs) and the inferior vena cava (which returns blood to the heart from the pelvis and legs) - are both located slightly to the right of the spinal cord and behind the uterus. As the uterus grows, it presses on these vessels. Lying on your left side allows the uterus to shift slightly away from the aorta and vena cava so that blood can move more freely through them, says Dr. Yvonne Thornton, director of the Perinatal Diagnostic Testing Center, at Morristown Memorial Hospital in New Jersey.If you can, rest for at least two hours a day on your left side, besides going to sleep that way. Your doctor may also prescribe additional left-sided rest if the fetus is progressing slowly or if you have a condition that can compromise blood flow, such as high blood pressure.