Why pregnant women should sleep on their left side

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Many doctors advise pregnant women to only sleep on their left side, but why? Is it dangerous to sleep on the right side or on your back?  

As the fetus gradually gets bigger, it starts to put more and more pressure on the mother’s internal organs and blood vessels.   The inferior vena cava (IVC), the large vein located on the right side of the spinal column,  is particularly sensitive to this pressure. This vein carries blood from the lower half of the body to the heart.  

If a pregnant woman is lying on her back, the fetus is more likely to compress the inferior vena cava, decreasing the amount of blood returned to the heart,” explained Grace Pien, assistant professor of medicine at the Johns Hopkins University School of Medicine, to Live Science. “There’s not a lot of research comparing sleeping on the right and left side, but at least theoretically, you’d also have less potential compression of the IVC on your left side than on your right.”

There will be naturally less blood pumped by heart if there is less blood being carried to it.  This results in a drop in blood pressure for the mother and a drop in the oxygen content in the blood for the mother and the baby as it is the mother’s blood which brings oxygen to the baby.  The body of healthy pregnant women can usually compensate for this cardiac output reduction.  However women with asthma or sleep apnea, for example, may have trouble oxygenating their baby. In some cases, the consequences can be serious.

A number of studies have suggested that sleeping on one’s back during late pregnancy may be associated with a higher risk for stillbirth,”  noted Grace Pein.  It’s for this reason that many doctors strongly advise all pregnant women to avoid sleeping on their back – at least for those who are used to it – and if they can to make an effort to sleep on the left side.  She added that it is “a relatively easy, cost-free intervention” which could prevent some very negative pregnancy outcomes.

However do be aware that that if you have a healthy pregnancy and find it too difficult to sleep on your left side there is probably nothing to worry about if you roll to the right. In fact, as Pein noted it may be better for you, as not getting enough sleep can be much worse for pregnancy than the slight risk of IVC compression when you are on your right side. 


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