GUIDE
Side sleeping — especially the left side — is the recommended position after 20 weeks of pregnancy.
Left-side sleeping optimizes blood flow to the placenta by keeping the weight of the uterus off the inferior vena cava (the large vein returning blood to the heart). Back sleeping after 20 weeks can compress this vein, reducing blood flow to you and the baby. But if you wake up on your back, do not panic — just roll to your side.
Be prepared from day one
As the uterus grows, it becomes heavy enough to compress the inferior vena cava — the major vein that returns blood from your lower body to your heart — when you lie flat on your back. This compression can reduce cardiac output by up to 25 percent, which means less blood flow to the placenta and less oxygen reaching the baby.
In practice, most people feel this compression as dizziness, lightheadedness, nausea, or shortness of breath when lying on their back. Your body is usually good at signaling you to move. But during deep sleep, you may not notice the discomfort, which is why the recommendation is to intentionally fall asleep on your side.
A 2019 study published in The Lancet EClinicalMedicine found that going to sleep on your back after 28 weeks was associated with a modestly increased risk of stillbirth. The absolute risk remains small, but the fix is simple: sleep on your side.
Either side is safe. Left is slightly preferred, but right is perfectly fine. The important thing is to avoid prolonged back sleeping after 20 weeks.
The biggest concern is back sleeping after 20 weeks. Stomach sleeping is fine until it becomes uncomfortable.
You do not need to buy a specialty pillow — regular bed pillows work well. But many people swear by pregnancy pillows for the convenience of a single setup.
If you wake up on your back, simply roll to your side. The fact that you woke up means your body signaled the problem. Brief episodes of back sleeping are not dangerous. Stressing about sleep position actually makes pregnancy insomnia worse, so give yourself grace. The goal is to fall asleep on your side, not to maintain a perfect position all night.
In the first trimester, any position is fine. The uterus is still tucked within the pelvis and is not large enough to affect blood flow. Sleep however you are comfortable — on your back, side, or stomach.
In the second trimester, start transitioning to side sleeping around 20 weeks. This is a good time to invest in a pregnancy pillow or set up your pillow arrangement. Getting used to side sleeping now makes the third trimester easier.
In the third trimester, side sleeping becomes essential. Most people naturally find that back sleeping is uncomfortable by this point. Use pillows liberally — between the knees, under the belly, behind the back, and under the head as needed.
If you are struggling to sleep despite good positioning, the issue may be pregnancy insomnia, back pain, leg cramps, or heartburn rather than position itself. Treating the underlying discomfort often does more for sleep than pillow adjustments alone.
For the complete picture of managing sleep during pregnancy, see our pregnancy insomnia guide. For safe medication options, see our pregnancy-safe medications guide.
This guide is for informational purposes only and is not a substitute for professional medical advice. Always consult your healthcare provider with any questions about your pregnancy.
