Most pregnant people can safely sleep on their stomach through the first trimester, roughly until 12 to 16 weeks. After that point, the growing uterus makes stomach sleeping increasingly uncomfortable and impractical, and most people naturally shift to a different position. There’s no single week where stomach sleeping becomes dangerous, but your body will give you clear signals when it’s time to stop.
Why the First Trimester Is Generally Fine
During the first 12 weeks of pregnancy, the uterus sits low in the pelvis, tucked behind the pubic bone. At about 12 weeks, the top of the uterus (the fundus) reaches roughly the same level as the pubic bone. At this size, lying face down doesn’t put meaningful pressure on the uterus. The baby is also surrounded by amniotic fluid and cushioned by the muscular uterine wall, so the small amount of pressure from your body weight poses no risk.
By around 16 to 20 weeks, the uterus has grown well above the pubic bone and into the abdominal cavity. At this point, stomach sleeping starts to feel like lying on a small melon. Most people find it physically uncomfortable enough to stop on their own, long before it could cause any circulatory issues.
The Real Concern: Blood Flow in Later Pregnancy
The bigger conversation around sleep position in pregnancy is actually about back sleeping, not stomach sleeping. As the uterus grows, it sits at the same spinal level (around the fourth and fifth lumbar vertebrae) as the inferior vena cava, the large vein that carries blood from your lower body back to your heart. When you lie flat on your back, gravity pulls the uterus backward onto this vein, potentially reducing blood flow significantly. The aorta can also be compressed. This is sometimes called aortocaval compression syndrome.
The same basic mechanics apply to stomach sleeping in later pregnancy, though by the time the uterus is large enough for this to matter, lying on your stomach is so physically awkward that almost no one does it. Your body essentially solves the problem for you through discomfort.
What the Research Says About Sleep Position Risk
A large meta-analysis published in eClinicalMedicine (The Lancet) found that going to sleep in a supine (back) position after 28 weeks was associated with 2.6 times higher odds of late stillbirth compared to sleeping on the left side. The researchers estimated that if every pregnant person at 28 weeks or beyond fell asleep on their side, late stillbirth rates could be reduced by about 5.8%.
An important reassurance from the same study: sleeping on your right side carried virtually the same risk as sleeping on your left. The adjusted odds ratio was 1.04, meaning there was no meaningful difference between the two sides. So while left-side sleeping is often presented as the “gold standard,” either side is equally safe.
Based on this evidence, the U.K.’s National Institute for Health and Care Excellence (NICE) advises trying to avoid going to sleep on your back after 28 weeks. This is the clearest guideline available, and it applies to your going-to-sleep position, not every position you find yourself in during the night. If you wake up on your back, simply roll to your side.
Warning Signs Your Position Needs to Change
Your body is surprisingly good at telling you when a sleep position isn’t working. If lying on your stomach or back causes any of the following, roll onto your side:
- Dizziness or lightheadedness
- Nausea
- Sweating
- Increased heart rate or a pounding sensation
- Pallor (looking unusually pale)
These symptoms result from reduced blood return to your heart and typically resolve within seconds of shifting to your side. They’re more common in the third trimester and tend to happen when lying flat on the back, but they can occur in any position that puts pressure on major blood vessels.
Why Left-Side Sleeping Gets Recommended
The inferior vena cava runs along the right side of the spine. Lying on your left side positions the uterus away from this vein, allowing unrestricted blood flow back to your heart. This benefits kidney function (your kidneys filter more efficiently when not compressed), reduces swelling in your legs and feet, and optimizes the amount of oxygen and nutrients reaching the placenta.
That said, the research is clear that right-side sleeping is just as safe as left-side sleeping in terms of stillbirth risk. The practical takeaway: sleep on whichever side is comfortable. Switching between sides throughout the night is perfectly fine and may actually help reduce hip and shoulder soreness.
Tips for Lifelong Stomach Sleepers
If you’ve always slept on your stomach, transitioning to side sleeping can feel frustrating, especially during a time when sleep is already harder to come by. A few strategies can help.
Place a pillow between your knees and another under your belly. This creates a slight forward tilt that mimics the feeling of stomach sleeping without putting pressure on the uterus. A pillow behind your back can also prevent you from rolling onto your back during the night. Full-length pregnancy pillows wrap around your body and serve all three functions at once.
Start practicing side sleeping before you need to. If you begin working on the habit around 12 to 14 weeks, you’ll have several weeks to adjust before stomach sleeping becomes uncomfortable and well before the 28-week mark when back sleeping becomes a concern. Some people find it easier to fall asleep on the couch or in a recliner during the transition period, since the semi-upright angle naturally prevents both stomach and flat-back positions.
If you wake up on your stomach or back, don’t panic. The goal is to start the night on your side. Your body will usually prompt you to shift positions if blood flow becomes restricted, and brief periods in other positions are not the same as spending an entire night that way.