Why is it better to sleep on your left side when pregnant?

Many women know that when they are pregnant you will be asked to sleep on your side instead of your back (or stomach) and that it is better to sleep on our left side and not on our right. What most women do not know, however, is the reason behind this. Even many of my pregnant friends knew there was a medical reason, but couldn't remember what that reason was.

So I thought I'd quickly explain the reasons in case you wanted to be reminded or learn about it for the first time.

The main reason is because we have a vein, called the vena cava, that is the main vein that drains the entire lower half of the body. It lies just to the right of your spine, so as the baby gets bigger and your uterus gets heavier, lying flat on your back will obstruct the vena cava's ability to flow up towards the heart. (Think of it as stepping on a garden hose) The drainage to the lower half of the body becomes sluggish, which not only increases the swelling of your ankles, feet, and legs, but will also impact on hemorrhoids as well. Decreased return of blood flow to the heart will cause lowered blood pressure and result in less blood flow to the uterus, placenta and hence your baby.

Some signs of low blood pressure (hypertension) are nausea and light headedness.

Lying on your left side is the best position of all because in that position you will have the least amount of weight on the vena cava. So even though lying on your right side is much better than lying on your back, that is why they tell you lying on your left side is the best.