Sleeping position – do pregnant women have to sleep on the left side only?

Many pregnant women read about the advice of sleeping on the left side from books. However, when they practised this, they either found it very difficult to sleep just on one side throughout the whole night or woke up every morning with discomfort over their left shoulder and back! Hopefully, this article can shed some lights on this important topic.

1. What sleeping position should be avoided?

Probably the supine position (sleeping on the back). The reasons are as follows:
  • At the supine position, the pregnant uterus can compress onto the inferior vena cava (the main vein within the tummy), which is located slightly to the right of the midline of the body. The compression results in a reduction of blood carried back to the heart, and hence a drop of cardiac output. Therefore, one may experience symptoms like headache, shortness of breath and nausea;
  • The blood supply to the fetus via the placenta may also be reduced;
  • The tongue is more likely to fall backward with the supine position and hence there is a higher chance of airway obstruction during sleep.


2. What is the theoretical benefit of sleeping on the left side?

  • The inferior vena cava is slightly to the right of the midline. The concern of sleeping on right is that the uterus may still compress onto this vein;
  • The aorta, which is the major blood vessel that carries oxygenated blood from the heart to the lower body, is located slightly to the left of the midline. It has thicker muscular vessel wall and is less compressible by the pregnant uterus. Therefore, some advocate to sleep on the left side.


3. What does the recent research say?

  • Some studies in the past have shown that sleeping at the supine position or on the right side is associated with adverse pregnancy outcomes including stillbirth. However, most of these studies are limited in that the sleeping position was asked following adverse outcomes in a retrospective manner, thereby subjected to a reported bias;
  • In 2019, a large prospective study on the sleeping positions involving over 9,500 pregnant women was published. The researchers have found no association between supine or non-left sleeping positions and adverse pregnancy outcomes.


4.What are the practical tips?

  • Avoid sleeping at the supine position if possible to prevent any potential caval compression;
  • If one notices that she is sleeping on her back when waking up, no need to worry as it is most likely alright;
  • Sleep on side, either left or right;
  • Try to support the back and the belly by placing one small pillow or cushion underneath respectively. Most find it more comfortable;
  • If one wants to sleep on the back, tilting the back slightly by placing a small pillow underneath on one side can help to avoid caval compression.
This article is contributed by Dr. T.N. Danny Leung
Updated on 25.09.2020