Lying on your stomach during pregnancy is safe in the first trimester and most of the second trimester. A large NIH-funded study of more than 8,700 women found that sleep position during early and mid pregnancy (up to 30 weeks) did not affect the risk of pregnancy complications, regardless of whether women slept on their stomach, back, or either side.
Why Your Baby Is Protected Early On
In the first trimester, your uterus is still tucked behind the pelvic bone, so lying face-down puts almost no pressure on it. Even as the uterus grows, the baby is surrounded by amniotic fluid inside the amniotic sac, which acts like a shock absorber. This fluid cushions the baby from your movements, whether you jump, fall, or press your weight against your abdomen during sleep.
The real limiting factor isn’t safety. It’s comfort. Most women find stomach sleeping physically awkward somewhere between 16 and 20 weeks simply because the belly gets in the way. If lying on your stomach still feels fine, there’s no medical reason to force yourself into a different position.
When Sleep Position Starts to Matter
The concern shifts after about 28 weeks, and it’s not about stomach sleeping. It’s about back sleeping. By the third trimester, the weight of the uterus can compress a major blood vessel called the inferior vena cava when you lie flat on your back. This compression can lower your blood pressure and reduce blood flow to the baby.
The data on this is striking. A meta-analysis of five studies involving over 3,100 pregnancies found that going to sleep on your back after 28 weeks roughly doubled the odds of stillbirth compared to falling asleep on the left side. Back sleeping also tripled the odds of the baby being born smaller than expected. The same analysis found no increased risk from sleeping on the right side or in any other non-supine position compared to the left side.
Stomach sleeping in the third trimester is essentially a non-issue for a different reason: it’s nearly impossible to do comfortably with a full-term belly.
Left Side vs. Right Side vs. Any Side
You may have heard that the left side is the only “correct” sleep position during pregnancy. The NIH study challenges that idea. Among the 8,700 women tracked, adverse outcomes were no more common among right-side sleepers or back sleepers than left-side sleepers, at least through 30 weeks. After 28 weeks, the key recommendation is simply to avoid falling asleep flat on your back. Sleeping on either side is fine.
What If You Wake Up on Your Stomach or Back
Rolling onto your stomach or back during sleep is normal and not something to worry about. Stanford Medicine’s guidance is straightforward: sleeping on your stomach is okay if it’s comfortable. Your body gives you reliable signals here. Discomfort, dizziness, or nausea will typically wake you up or prompt you to shift before any harm is done. If you wake up on your back in the third trimester, just roll to your side and go back to sleep.
Practical Tips for Comfortable Sleep
As stomach sleeping becomes less feasible, a few adjustments can help. A pillow between your knees while side-sleeping takes pressure off your hips and lower back. A wedge pillow tucked under your belly provides support so you’re not pulling on your abdominal muscles. Some pregnancy pillows are shaped like a C or U and wrap around your entire body, keeping you propped on your side without conscious effort.
If you’re a committed stomach sleeper who misses the position, some women find that hugging a body pillow while angled slightly forward gives a similar sensation without putting direct weight on the belly. This “semi-prone” position is perfectly safe and can feel more natural than lying flat on your side.
Sleep quality tends to decline as pregnancy progresses regardless of position, thanks to frequent urination, heartburn, and general discomfort. Prioritizing whatever position lets you actually fall asleep and stay asleep matters more than chasing a theoretically perfect alignment, with the one exception of avoiding flat-on-your-back sleeping after 28 weeks.