If I’m going to talk about sleep, I need to start with the whole “sleeping on the left side while pregnant” issue. I am shocked by how many students come in and have been told by their care provider that it is important to sleep on their left side, but have never received an explanation as to why. It is too often that a very concerned student asks me if she hurt her baby because she woke up on her back. So why the left side? It is because of Vena Cava Syndrome. The inferior vena cava (a large vein that is responsible for the venous return from the lower half of the body back to the heart) runs slightly to the right of the aorta. When compressed by the weight of the baby, the blood return is compromised and the mother may feel light headed and nauseated. Think of the vena cava as a big hose, and the baby as a foot stepping on the hose. When the hose is compressed, the water can’t flow out- same idea as vena cava syndrome. This is easily remedied by moving so that the baby can roll off the vena cava. Since this vein is located on the right side of the body, it is recommended as the baby gets bigger, the mother sleeps on her left side. For some women, this never becomes an issue and they can sleep however they like throughout their pregnancy. Others are more sensitive to this and must modify their sleep position. As mentioned earlier, it is not necessarily dangerous if you wake up on your back. Bodies are smart, and signal the mother with signs of light headed-ness, nausea, heaviness in the chest or breathlessness.