4 Charts: 3rd Trimester Sleeping Positions Ranked | Visualized Science

Reviewed by The Clinical Committee

June 05, 2019

  • Sleeping on the left and right are the safest during the 3rd trimester.

  • Sleeping on the back increases the risk of stillbirth.

  • Sleeping on the left and right are statistically equivalent according to a new meta-analysis.

Sleeping on your back during the 3rd trimester

Sleeping on your back during the 3rd trimester

Figure 1: Sleeping on your back during the 3rd trimester. A meta-analysis covering 6 studies which included 851 cases of still birth alongside 2,257 matched controls showed that sleeping on the back during the 3rd trimester can be dangerous to the fetus. Researchers estimated that 5.8% of cases of stillbirth are caused by sleeping on the back.

As if pregnancy wasn’t already hard enough, it turns out how someone sleeps during pregnancy can play a big role in a fetus’ health.

A new meta-analysis covering six major studies has shown that sleep position strongly correlates with fetal health.


Meta-analyses systemically combine data and findings from a selected group of studies on a particular topic to create conclusions with higher statistical significance. These studies do not typically add new data, but rather use data that has already been produced by others. With good methods, they can find more robust and accurate results as they include more data. They can put together conflicting conclusions from smaller studies to create a "final answer."" However, these studies can include bias if inappropriate studies are analyzed. Additionally, they can suffer from publication bias, where only positive results are published and included in the analysis.

Researchers estimated that sleeping in the wrong position is responsible for nearly 6% of all stillbirths.

Source: An Individual Participant Data Meta-analysis of Maternal Going-to-Sleep Position, Interactions with Fetal Vulnerability, and the Risk of Late Stillbirth

Data on Sleeping Position & Pregnancy

Data on Sleeping Position & Pregnancy

Figure 2: Data on Sleeping Position & Pregnancy. Reseearchers estimate that sleeping on your back during the 3rd trimester increases risk of stillbirth by 263%. Other risk factors, such as high blood pressure and diabetes, were found to increase risk by 223% in the same study.

Sleeping on your back increases risk of stillbirth by around 260%, even after adjusting for multiple varibles.

This is similar to the increase of risk from other factors such as high blood pressure and diabetes which can impact childbirth and pregnancy.

Mechanism of Risk

Sleeping on the back reduces blood flow to and from the heart. While this generally is not an issue for non-pregnant individuals, pregnant women require a lot more blood for the uterus. Sleeping on the back is believed to reduce blood flow to the uterus, which reduces the amount of oxygen and nutrients available for the developing fetus.

Sleeping on the left versus the right

Sleeping on the left versus the right in pregnancy

Figure 3: Sleeping on the left versus the right in pregnancy. The meta-analysis found that across 6 studies, there was no statistically significant relationship between sleeping on the left vs the right and risk of stillbirth.

Unequivocally, sleeping on the side is better. But does it matter if you sleep on the left or the right?

According to the data, both are just as good. However, as new data comes out, it is possible that we will see one becoming better than the other.

While some doctors have published opinions preferring the left, the data generally shows that both are statistically equivalent.

What about sleeping on the back?

By the third trimester, sleeping on the back becomes uncomfortable for most women and most choose other sleeping positions. Therefore, there is insufficient evidence to make a determination. Since we know that sleeping on the left and the right are safe, and that sleeping on the back is not safe, we rank this is number three among the sleeping positions.

Keys to Health

Best Sleeping Positions in Pregnancy

Figure 4: Best Sleeping Positions in Pregnancy. The best sleeping positions during pregnancy are on the left side or the right side. Sleeping on the left has been endorsed by some doctors, but the evidence has not fully supported this theory yet. Sleeping on the back in the 3rd trimester is a known risk factor for still birth. There is insufficient data regarding sleeping belly-side down.

Evidence Score:


Variable Adjustment - The researchers use the multi variable adjustments in their analysis which provides better data with less potential of bias


Strength of Findings - The findings provide strong and statistically significant evidence for sleeping position and safety.


Study Selection - Researchers used good methodologies in selecting studies. The selected studies had similar patients and selection criteria.


Sample Size - This study used relatively few patients for a meta-analysis, which opens up the possibility for bias and reduces the quality of the findings.


Study Type - While meta-analyses are generally a good method, they are only as good as the underlying studies that they cover. The studies in this meta-analysis used case-control methodology which can be more prone to bias than a prospective cohort or a clinical trial.

Expert Opinions

American Pregnancy Association

The best sleep position during pregnancy is “SOS” (sleep on side). Even better is to sleep on your left side. Sleeping on your left side will increase the amount of blood and nutrients that reach the placenta and your baby. Keep your legs and knees bent, and put a pillow between your legs.

Mayo Clinic

Favor your side. Avoid sleeping on your back, which can put the weight of your uterus on your spine and back muscles. But don't worry if you wake up on your back.

University of Rochester Medical Center

The best sleeping position during pregnancy is on your side. The left side is especially good because it lets the most blood flow to the fetus. It also improves your kidney function.

Clearvue Health is not affiliated with above organizations. The information above is provided to highlight and link to useful further reading.

Further Reading: Hospital Choice & Safety for Mothers

Hospital Size Matters for New Mothers

Childbirth is one of the riskiest events in a woman's life. New research is showing that your choice of hospital matters.

A new study suggests that your choice of maternity hospital can play a big role in your odds of a safe medical delivery or C-section. Delivery complications have risen in recent years. Larger hospitals that deliver more babies tend to provide better outcomes.

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