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.
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 (which you can obtain by propping up your right side with a pregnancy pillow or a regular pillow) has been shown to reduce the risk of low blood pressure.
For me, sleeping in with my right side slightly propped up felt pretty safe. But mostly, it felt comfortable.
Did you avoid lying on or sleeping on your back during pregnancy?
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!
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.
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.
Good for you! We all need to sleep comfortably as possible, especially before we have a newborn waking us up at night.
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!
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.)
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
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.
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
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…
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!
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 😀
You’re welcome!
I am totally miserable today due to sharp pains in my right thigh and hip from sleeping on my side (when I would normally sleep on my back). I am literally limping all day. Pregnancy pillow + 2 cushions got me through the 2nd trimester but now in the 3rd trimester I am in so much pain from sleeping this way. Stumbled upon this blog because I went looking for someone, anyone, anywhere, to tell me that it can’t possibly be *that* unsafe to sleep on your back!! Funnily enough I have previously read the New Zealand data elsewhere and the part about getting up to the bathroom jumped out at me, as well. I rarely have to get up to go in the night and don’t understand why this would be a cause for concern. I have 11 weeks to go and cannot bear the thought of being in this much pain throughout. I also don’t see how it can be beneficial to me to have this much hip/thigh pain during pregnancy and then ultimately whilst giving birth. Thanks for presenting some perspective. Best, H.
Christine, thank you so much for writing this and giving some perspective. Having previously miscarried I have been torturing myself during this pregnancy trying to sleep on my left hand side despite severe hip bursitis – with resulting sleepless nights! Can I ask, when you say you slept at a tilt using a pregnancy pillow, did you mean you slept with a slight lateral tilt? I’ve been trying to picture the sleeping position you mean as I can’t quite visualise it but would like to reproduce it for myself and get a bit more sleep!
That sounds rough. Propping up your back with a pillow, so you are not lying flat, propping up your right hip with a pillow will give you enough of a life to prevent compression.
Thank you so much, Amy (and apologies for calling you ‘Christine’ – must be the sleep deprivation!)
This week, at 23 weeks pregnant, I have fractured my hip from sleeping in my left side from all that information. My ob believes a woman will move in her sleep if something is pressing g and cutting if circulation to anywhere in your body and I’m an at least now for 4 weeks, totally unable to sleep on my left anyway. I think these researchers need to contemplate what they are actually asking of our bodies when they put this information out. It’s not natural, and now what’s worse? A broke hip, or possibly getting a bit fainty, which I haven’t experienced on my back at all anyway? Great article, and I will be sleeping as comfortably as I can, and without being silly about it from now on.
Thank you so much its a relief to know that i’m not just the one experiencing the burden of what proper position should i need to do while sleeping, which ends me not able to sleep at night. I am more comfortable in sleeping in my back than doing the side lying positions which numbs my hands and leaves hip pain to me.
It is my first pregnancy that is why ‘am
So nervous on what should i need to do and asked a lot of advices which confuses me already but after reading this article, it took the bean in my throat knowing that ‘am
Not doing wrong and we (my baby) is safe.
Thank you so again.
Thanks so much for writing this article. Gives me peace of mind knowing that the risk of sleeping in the back is low. Thank you for doing the research and writing about it – 5 years on and people still commenting means it’s still a valid concern for pregnant women.
I’m 6 weeks away from my due date and reading this in the middle of the night because I literally cannot sleep on my side anymore. I used to sleep on my tummy before I was pregnant and since the start of the pregnancy I have been told to sleep on the left side. My masseuse friend tells me how messed up my hips are from doing this, and the nerve pain down my legs keeps me tossing and turning to the point where I give up trying to sleep at all. So happy to read this article, thank you for doing the research! I am so much more comfortable on my back or at least switching to it for a period of time. Maybe now I can stop experiencing this seemingly neverending insomnia..
You’re welcome! And I hope your insomnia eases up. I’m no stranger to sleepless nights and they are the worst!
I am 18 weeks 4 days pregnant and I just woke up with hip pain after a night forced to sleep on my sides, even though I changed the sides a few times during the night and even slept a bit on my back. The pain is not too bad yet but I am scared it will just get worse with time if I go against my natural instincts and force myself to sleep on my left side only. I never ever felt any problems laying on my back during my pregnancy: no feeling faint, no feeling breathless and my tummy does not feel heavy nor pressing against anything. I doubt that I am one of those very few women who would have any blood flow problem lying on my their backs.
Also, when my obstetrician checked the blood flow to my placenta last time, I was lying on my back, and blood flow was good!
Great article!
Thank you so much for this well-written article and well-researched topic! I’m in week 24 and have had hip pain from sleeping on my sides. Funny thing is, I’m generally a side sleeper (when not pregnant). No matter how hard I try to sleep on my sides, I end up on my back, and I feel really comfortable! Your article has helped put me at ease with this. My doctor also eased my mind about it by telling me that it really isn’t THAT big of a deal if I wake up on my back. Thanks for the great article!
Thank you for this article. It’s frustrating how little the docs will tell you about how to know or sense if you are putting yourself or baby at any kind of risk. I’ve stressed over how long, 5 mins? 20 mins? is too long to rest on my back while it’s the only comfortable position.
I am still trying to figure out why I had gestational hypertension. This happened with two of my pregnancies. I have always been a back sleeper. The condition is not existing in my family. Could it be because of sleeping on my back? (my babies are both in health condition)