Why Sleeping On Your Side Is Good For Your Baby

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Research proves that sleeping on your left lateral recumbent position, or simply sleeping on your left side actually decreases the risk of stillbirth.

Stillbirth is a tragic outcome for families and may be the most feared consequence of pregnancy. It remains a serious public health concern in many countries including the United States. Fortunately, it is considered as one of the few potentially avoidable maternal and child health problems.

Centers for Disease Control and Prevention (CDC) defines stillbirth as the death or loss of a baby before or during delivery. It is sometimes associated with the concept of miscarriage because both terms indicate the loss of pregnancy. However, the two differ in their timing.

As the CDC describes it, a miscarriage in the United States is usually defined as a loss of a baby before the 20th week of pregnancy. Meanwhile, a stillbirth is the loss of a baby after 20 weeks of pregnancy. Also, stillbirth is classified into early (fetal death occurring between 20 and 27 weeks of pregnancy), late (between 28 and 36 weeks), and term (between 37 or more weeks).

Globally, there were 2.6 million reported cases of stillbirths in 2015 based on statistics from the World Health Organization. That’s around an estimated 7,178 babies dying each day. Ninety-eight percent (98%) of these cases occur in low- and middle-income countries. 

Risk factors for stillbirth are usually not avoidable such as advanced maternal age—for women over 40 years old,—obesity, cigarette smoking, a poorly growing fetus, first pregnancy, and having three or more babies.

However, most of the reasons for stillbirth are commonly due to a woman’s biology, which led the research on other possible risk factors like a woman’s habit or behavior.

A study from The University of Auckland revealed that a pregnant woman’s going-to-sleep position is crucial in preventing stillbirths.

This 2011 Auckland Stillbirth Study was the first of its kind and stated that there was an association between maternal sleep-related practices and late stillbirth (≥28 weeks of pregnancy). 

The findings of their study showed that women who slept on their back were more likely to experience a late stillbirth compared with women who slept on their side.

According to lead author Professor McCowen, pregnant women who sleep lying on the back during the last three months of their pregnancy was associated with a 2.6-fold increased risk of stillbirth compared to those who sleep lying on the side. However, she reassured that it is the going-to-sleep position which is significant and not the position when they wake up.

In addition, the study confirms that both left and right sides are equally safe so the mother may choose whichever side she wants. According to Obstetrician Gynecologist Dr. William Milford, the previous reason for the left-sided sleeping was due to the anatomical position of the inferior vena cava (IVC), which is the blood vessel that brings most of the blood flow from the lower half of the body back to the heart. This is because the IVC is located on the right side of the spinal column so it is less likely to be compressed when pregnant women lie on their left side.

A meta-analysis combining the findings of five previous stillbirth studies (including the 2011 Auckland Stillbirth Study) utilizing information from a total of 851 bereaved mothers and 2,257 pregnant women was done by researchers from the University of Auckland. To date, this is considered as the largest study conducted regarding the association of maternal sleeping position with the risk of late stillbirth.

The other four studies included in the meta-analysis were a multi-center study from Aotearoa New Zealand, one from Australia, one from the United Kingdom and one from the United States. This study was headed by Professor Lesley McCowan, the Head of the University’s Obstetrics and Gynecology.

However, this was countered by other researchers showing that the IVC is actually not compressed while lying on your side but becomes compressed when lying on your back. This reduces the blood flowing towards the heart by about 80%. Moreover, the aorta, which is the main artery of the mother from the heart, is slightly compressed in this position which leads to a reduction in the blood flow going towards the baby by about 30%.

The findings emphasized that this is significant only in pregnant women who are on their last three months of pregnancy (third trimester) which is after 28 weeks of pregnancy and not earlier than this. The main reason is that at first and second trimester, the uterus is still relatively small and could not readily compress the blood vessels, therefore having none or less impact on reducing the blood flow towards the fetus.

The researchers of this study stated that if all pregnant women in their third trimester resorted to sleeping on their side, this could potentially reduce the cases of late stillbirth by about 6%. This means saving at least 130,000 babies each year worldwide. Generally, doing preventive measures as simple as changing your going-to-sleep position might be saving your baby’s life.

Photo: Bart Everson

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