Sleeping on your right side during pregnancy is not dangerous, and the concern is often overstated. The real position to avoid after 28 weeks is sleeping flat on your back, which can compress a major blood vessel and reduce blood flow to your baby. Right-side sleeping does compress this vessel slightly more than left-side sleeping, but the difference is far smaller than many pregnancy forums suggest.
What Happens to Blood Flow When You Lie Down
The concern centers on the inferior vena cava, a large vein that runs along the right side of your spine and carries blood back to your heart from your lower body. As your uterus grows heavier in the second and third trimesters, it can press against this vein when you lie in certain positions. Lying flat on your back creates the most compression, because the full weight of the uterus sits directly on the vessel. This can reduce the amount of blood returning to your heart, which in turn reduces blood flow to the placenta and your baby.
An MRI study comparing sleep positions in pregnant women found that lying tilted to the left at 30 degrees kept the inferior vena cava significantly more open than tilting to the right at either 15 or 30 degrees. The average volume of the vein was roughly 10.7 mL in the left-tilt position versus about 5.9 mL in both right-tilt positions. That’s a measurable difference, and it’s the anatomical basis for the common advice to sleep on your left side. But “more compression than left” is not the same as “dangerous.” The right side still takes pressure off the vein compared to lying flat on your back.
What the Research Says About Risk
The strongest evidence links back sleeping after 28 weeks to a modest increase in stillbirth risk and babies born smaller than expected. A large pooled analysis of multiple studies found this association with going to sleep on your back, not with right-side sleeping. In fact, one major review noted that going to sleep on the right side was not associated with increased risk of late stillbirth. The relationship between back sleeping and stillbirth held even after accounting for factors like obesity, smoking, and fetal size.
Based on this evidence, clinical guidelines advise pregnant women to try to avoid falling asleep on their back after 28 weeks. They do not advise against sleeping on the right side. The left side is considered the ideal position because it maximizes blood flow, but the right side is a reasonable alternative and far preferable to sleeping on your back.
When Sleep Position Starts to Matter
Sleep position does not appear to affect pregnancy outcomes during the first or second trimester. A large NIH-funded study followed more than 8,700 women and tracked their sleep habits between weeks 6 and 13, then again between weeks 22 and 29. Sleeping on your back or either side through 30 weeks showed no increased risk of stillbirth, reduced birth size, or blood pressure complications. The researchers noted that their findings only covered sleep through 30 weeks and couldn’t speak to the final weeks of pregnancy.
The guidance to favor your left side kicks in around 28 weeks, when the uterus is heavy enough to meaningfully compress blood vessels. Before that point, sleep however you’re comfortable.
If You Wake Up on Your Back or Right Side
One of the most common worries is waking up in a position you didn’t fall asleep in. This is normal and not something to panic about. Your body has built-in warning signals: if your baby were actually at risk of reduced oxygen from your sleeping position, you’d feel nauseated, dizzy, or breathless well before any harm occurred. Most women never experience low blood pressure from back sleeping, so waking up on your back occasionally is unlikely to cause problems.
What matters most is the position you fall asleep in, since that’s the position you spend the longest stretch of the night in. If you drift onto your back or right side during the night, simply roll back to your left when you notice. If it keeps happening, a partner can gently reposition you, or you can use a pillow behind your back as a physical reminder to stay on your side. The last thing you need during pregnancy is another source of nighttime anxiety. Rest itself is valuable, and losing sleep over your sleep position does more harm than occasionally ending up on the wrong side.
Staying Comfortable on Your Side
Side sleeping gets harder as pregnancy progresses, especially if you’re dealing with hip pain or a belly that feels heavy and unsupported. A few simple adjustments can help. Place a pillow between your knees to keep your hips level and take pressure off your joints. This single change often resolves the hip and lower back pain that makes side sleeping miserable. Tucking a pillow behind your back provides support and acts as a barrier against rolling onto your back during the night.
Full-length pregnancy pillows are popular because they support your arms, belly, and legs simultaneously, keeping everything aligned without needing to arrange multiple pillows. If you don’t want a specialty pillow, a regular pillow under your belly and another between your knees accomplishes much of the same thing. Experiment with pillow firmness too. Memory foam holds its shape and keeps your knees separated all night, while softer fills like down alternatives may feel more comfortable but flatten over time. The best setup is whichever one lets you fall asleep on your side without waking up sore.
The Bottom Line on Right-Side Sleeping
Left-side sleeping is the gold standard because it keeps the inferior vena cava most open, maximizing blood return to your heart and oxygen delivery to your baby. Right-side sleeping compresses this vein somewhat more but is not associated with increased stillbirth risk in the research. Back sleeping after 28 weeks is the position with the clearest evidence of harm and the one worth actively avoiding. If you find yourself more comfortable on your right side some nights, that’s a perfectly reasonable place to sleep.