It’s (Probably) Safe to Sleep on Your Back While Pregnant

Can you safely sleep on your back while pregnant? Here’s what the latest research has to say.

My third trimester in my second pregnancy was rough. The days were fine, but the nights were awful. I could not fall asleep. I was too uncomfortable. And as a second time mom, I was desperate. Months of sleep deprivation were my certain future. Pregnancy was supposed to be an opportunity to stock up on sleep before the newborn period.

The only remotely comfortable position was lying on my back, propped up with a couple of pillows. But several pregnancy websites and and my OBs had warned me against sleeping on my back during pregnancy.

More than anything, I wanted to disregard this advice. But I needed to know how big a risk, if any, I would be taking by sleeping on my back.

My OBs were not helpful in this regard. Within the same clinic, one OB told me to avoid lying on my back from 4 months on, another told me to avoid this position from 7 months on, and a third said not to worry until the last month of pregnancy. When asked, none of them could tell me the magnitude of the risk.

Eventually, I dug into the research myself. Once I did, I understood why the advice is confusing to mothers: the underlying research is a mess.

The rationale for this prohibition is simple enough: lying on one’s back can cause supine hypotensive syndrome, sometimes known as aortocaval compression syndrome.

A pregnant woman woman’s belly can compress the inferior vena cava, a large vein running under the right side of her uterus; and compression of the inferior vena cava can cause a drop in blood pressure. In rare cases, the drop in blood pressure is severe enough to reduce heart output, lower oxygen going to the brain, and cause fainting.

Although the drop in blood pressure is unlikely to harm the mother, the concern is that if a pregnant woman’s oxygen levels drop, her baby’s might too. Under normal circumstances, though, women typically become uncomfortable and change their position before their blood pressure takes a serious dip.

lateral versus supine

Supine hypotensive syndrome has been reported as early as the second trimester, but it is mainly a problem of late pregnancy, after 36 weeks or so.

Despite how scary this sounds (“I might be depriving my baby of oxygen without knowing it”), according to a recent research review, back sleeping is safe for the vast majority of pregnant women. The reviewers build a compelling case: First, only very small percentage of pregnant women experience low blood pressure when lying on their back. Even among those women, the changes in their blood pressure do not appear to affect the fetus. Studies have found no effects on fetal blood flow or on fetal well-being during non-stress tests.

Second, the symptoms of low blood pressure (dizziness, nausea, a rapid heartbeat) are easily recognizable. Women can figure out for themselves if lying on their back makes them uncomfortable, and avoid the practice if it does. In the reviewers words:

Advising women to sleep or lie exclusively on the left side is not practical and is irrelevant to the vast majority of patients. Instead, women should be told that a small minority of pregnant women feel faint when lying flat. Women can easily determine whether lying flat has this effect on them, and most will adopt a comfortable position that is likely to be a left supine position or variant thereof.

Third, previous research did not examine back sleeping. The research only addressed positioning women during surgery, when they are completely immobilized and unable to change their position.

This review was written in 2007. Its conclusions are clear and reassuring. Unfortunately, since its publication, two more recent studies muddy these waters a bit.

The first study was conducted at a maternity ward in Ghana. Two hundred twenty women who had recently given birth reported their sleep practices during pregnancy. Compared to women who slept in another position, the 21 women who reported either sleeping on their backs or “backs and sides”, had higher rates of NICU admissions (36.8% vs 15.2%) and stillbirths (15.8% vs 3.0%), and were more likely to have given birth to an underweight baby (36.8% vs 10.7%). Even when the researchers controlled for the mother’s age, number of children, gestational age, and pre-eclampsia, these differences remained statistically significant.

The second study was conducted in New Zealand. Researchers interviewed 155 women who experienced unexplained late stillbirths (after 28 weeks) about their sleep position both before pregnancy and in the last month, the last week, and the last night before their pregnancy ended. Their responses were compared to 301 control women, who were a similar number of weeks along but with ongoing pregnancies.

The researchers carefully controlled for several known risk factors for stillbirth: obesity, smoking, low socioeconomic status, maternal age, and number of prior children. Even so, sleeping on one’s back the night before corresponded to a higher risk of a late stillbirth compared to sleeping on one’s left side.

In fact, sleeping on one’s right side or in any other position than on the left side correlated with a higher risk of stillbirth.

Considered together, these two studies seem reason for caution, but not fear. They have a number of problems. Both were quite small, and both relied on women’s ability to recall what positions they slept in. And for the Ghana study, it’s unclear how the findings translate to women in a high income country.

Even assuming these findings hold up, the absolute risk appears to be very, very low. In the New Zealand Study, during its 3-year study period, the rate of late stillbirth was 3.09/1000. The researchers estimate that left side sleeping would lower the risk to 1.93/1000, whereas right side or back sleeping would raise it to 3.93/1000.

To put this risk further in perspective, the New Zealand study also found that going to the bathroom an average of once a night or less (as opposed to two or more times) was associated with an increased risk of a stillbirth. This magnitude of the increase was comparable to back sleeping. Yet, based on these data, no one has proposed that pregnant women should wake up more often to go to the bathroom.

So, what are we to make of these data? In my personal opinion, the research is not strong enough to support blanket warnings against back sleeping. Yes, there is a plausible mechanism for back sleeping causing problems. But the bulk of the evidence suggests that compression of the vena cava very rarely causes problems.

Depending on her risk tolerance and ability to sleep, one woman might look at these data and feel fine sleeping on her back. Another might choose to sleep exclusively on her left side. Both seem like reasonable decisions.

For me, sleeping with a pregnancy pillow, resting mostly but not completely on my back was the right choice. In part, this was because I wanted to be conservative: A tilt of 10 degrees (such as from propping with a couple of pillows) has been shown to reduce the risk of low blood pressure. This position felt pretty safe. But mostly, it felt comfortable.

Did you avoid lying on or sleeping on your back during pregnancy?

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Author: Amy Kiefer

I am a research scientist and mother of three munchkins. I live in the Bay Area and when I am not child wrangling and catching up on lost sleep, I love digging into the research on all things fertility, pregnancy, and breastfeeding related.

17 thoughts on “It’s (Probably) Safe to Sleep on Your Back While Pregnant”

  1. I just wanted to thank you for your blog. I’m still working through the infertility bit myself, but I’ve gotten so frustrated with the lack of real information and almost condescending lack of science behind any of the discussions available on the internet or with my drs. I’m an engineer, it drives me crazy I can’t get my hands on real data and information when making such big decisions. So please keep writing!

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  2. Thanks, Chris! I know exactly what you mean. The information is often so dumbed down that it feels infantilizing.

    BTW, I have some fertility related posts coming soon that might interest you.

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    1. Exactly, infantilizing. As if women weren’t able to sense their own bodies and shift as they needed to. I had incredible hip pain from sleeping only on my sides while pregnant. It was terrible. I don’t count on doing it when I have my second child.

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  3. Thank you for sharing your research! I’m currently in my second trimester and have been told to begin sleeping on my left side. I have to admit, many nights I wake up on my back wondering how long I’ve been that way and worried that I’m hurting the baby. The truth is, like you said, it’s just so much more comfortable! I got a pregnancy pillow also. It has been a big help, but still nothing compares to my pre-pregnancy sleep comfort.

    Will you be discussing epidural vs natural birth at all in upcoming posts? Thanks again for sharing!

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  4. Thanks for your research, Amy!
    While pregnant I often thought about my mother and grandmother…did they avoid sleeping on their backs with all of their 11 (combined) healthy pregnancies?
    When did this tale of back sleeping risk become so prevalent? Was it one research study and suddenly all OBs are telling women to sleep on their left side?
    It almost seems like that’s what happens with a lot of “dangers” around pregnancy. That if some research suggests there’s even the slightest chance that something you’re doing could cause problems for the baby, doctors across the board will tell every patient not to do it and, as a patient who wants a solid explanation and evidence around it, I find this aggravating.
    (Writing on iPhone so I apologize for any typos, errors, etc.)

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  5. am 6months pregnant but have found lying on my back the most comfortable position because I had no other comfortable position but at 4 months my lower back could severely pain whenever I woke up but but later stopped and i still don’t know what caused the pain

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  6. Well done great article! I would like to add that they state that the weight of the baby causes compression of the vena cava and therefore causes the mother to have low blood pressure or to even pass out. If you think about the the TV program – My 600lb life. They are constantly on there backs and the weight of their fats far out weights the weight of an unborn child at 9 months. But these big people rarely pass out and are physically unable to sleep on their left side.

    Just my 2 cents worth.

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  7. i m 25 weeks pragnant and i just feel comfortable with the back side and midwifes said u should not sleeep back side but for me its very comfortable to sleep back side i m very confuse to sleep back side now coz i after i heard this i cant sleep from the 5 days what should i do i m feels very scary to heard this thing

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  8. I try not to sleep on my back, but I can’t help it! I fall asleep on my side and still end up on my back. When I wake up in the middle of the night, I will go to my side again, but in the morning I end up waking up on my back, hands behind my head just like I usually sleep. I guess I won’t actually worry too much about it though! Puts me a little at ease, although that difference in stillbirth is a little concerning to me…

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    1. Correlation does not prove causation… every good statistics class should teach this. To ask someone who had a still birth after the fact which way they slept the night before? Think about it… not very scientific!

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  9. The observational studies did not address maternal weight gain, or birthweight as a confounder. I suspect that mothers who had gained more weight (had larger babies or larger support systems for their babies) were less comfortable on their backs. That would be a non-causal explanation for the findings.

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  10. Thank you!!
    I am 26 weeks pregnant and write this at 3am as sleeping on my left side is almost impossible and I have been through sleepless nights scared of sleeping in my back.
    Being on my back and right side are the only comfortable positions for me and I have been denying myself the rest based on the myth that lying on my back is harmthful.
    Thank you so much for taking the time to do the research and sharing it.
    I am off to a good night sleep (finally!) now 😀

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