Why should you sleep on your side in the third trimester?
Going to sleep on your side from 28 weeks is linked to a lower risk of late stillbirth. In a UK study, going to sleep on the back was linked to 2.3 times the risk of going to sleep on the side. Stillbirth is rare, and either side is fine. If you wake up on your back, just roll over.
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What the research found
The UK's MiNESS study compared 291 pregnancies that ended in stillbirth with 735 that ended in a live birth. After 28 weeks, going to sleep on the back was linked to 2.3 times the risk of late stillbirth compared with going to sleep on the side.
Two things keep this in proportion. Stillbirth is rare: about 1 in 225 pregnancies in the UK. And MiNESS was an observational study, which shows a link rather than proof. A 2019 editorial in the journal eClinicalMedicine summed up the evidence as "time to act but with care." ACOG, the US obstetricians' group, also advises avoiding long periods lying flat on your back in pregnancy.
So why do it? Because the change costs nothing. Going to sleep on your side is free and easy.
Exactly what to do
- Go to sleep on your side from 28 weeks, at night and for naps.
- Either side is fine. MiNESS found no difference between left and right. You may have heard that the left side is best; this study didn't find a difference, so pick whichever is comfortable.
- If you wake up on your back, don't panic. Roll onto your side and go back to sleep. The studies looked at the position women fell asleep in, because that's the one you hold longest.
- Ask your midwife or doctor when to start if you're unsure.
Many parents feel guilty about nights they woke up on their back. Please don't. Nobody controls their position while asleep, and the advice is about how you settle in.
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Make side sleeping easy
A little setup makes this automatic. Build a pillow fort:
- One pillow between your knees.
- One pillow behind your back, so you can't roll over easily.
- One small pillow under the bump for support.
A long body pillow can do all three jobs. Set it up before 28 weeks so it already feels normal when it matters. And if you nap on the couch, use a cushion behind you there too.
| Situation | What to do |
|---|---|
| Falling asleep at night | On either side, pillow behind your back |
| Afternoon nap | Same rule: on your side |
| Woke up on your back | Roll onto your side and go back to sleep |
| Resting or exercising | Avoid long periods lying flat on your back |
What about lying on your back while awake?
The stillbirth research is about the position you fall asleep in. For awake time, ACOG's advice is to avoid long periods lying flat on your back in pregnancy. In practice:
- In prenatal yoga or Pilates, skip long poses flat on your back, or ask the teacher for a side-lying or propped version.
- When you exercise, choose positions where you're upright, on your side or on hands and knees.
- Reading in bed or watching a show? Prop yourself up with pillows, or lie on your side.
A minute on your back to get comfortable, or during a checkup, isn't what the guidance is about. Our page on exercise in pregnancy lists which activities are usually fine.
Small sleep wins for the third trimester
Pregnancy sleep is its own sport: heartburn, a tiny bladder, leg cramps and a baby who throws a party at 2 a.m. A few things help:
- Keep the same wake-up time most days, even after a bad night.
- Eat dinner a little earlier, and prop your head up if heartburn wakes you.
- Drink plenty of water during the day and taper off in the evening.
- Ask your partner to take the early alarm, the dog or the toddler a few mornings a week.
- Put the phone across the room.
If you snore loudly, wake up gasping, can't sleep most nights, or have strong urges to move your legs at night, mention it to your doctor or midwife. These are worth raising, not suffering through. Poor sleep and stress feed each other; our page on stress in pregnancy has a 10-minute evening routine that ends with you settled on your side.
Side sleeping and movements go together
Late pregnancy has two simple safety habits, and they work as a pair: go to sleep on your side, and know your baby's movement pattern.
If your baby is moving less than usual, call your doctor, midwife or labor unit now, day or night. Don't wait until morning to see if it improves, and don't rely on a home heartbeat monitor to reassure yourself. If you can't reach anyone, call 911. Our page on baby movements explains what to watch for.
Both habits support the same goal: helping your pregnancy reach term safely. The third trimester is when the baby's brain grows fastest, roughly four-fold, and every week in the womb counts.
After the birth: safe sleep flips
Once your baby is born, the rule flips for them: babies go to sleep on their back for every nap and every night, on a firm, flat surface in their own crib or bassinet, with nothing soft in it: no pillows, blankets, bumpers or toys. Keep the bassinet in your room for at least the first 6 months. It's worth setting up the safe sleep space now, in the third trimester. See baby sleep by age for the full rules.
Do this
- Set up a pillow fort tonight: one between your knees, one behind your back, one under the bump.
- From 28 weeks, settle on your side every time you go to sleep, naps included.
- If you wake on your back, roll onto your side without worrying.
- Save your labor unit's number in your phone and call right away if movements slow.
- Mention loud snoring, gasping or constant poor sleep at your next visit.
When to ask your doctor
Check with your doctor or midwife first if…
- You have a medical condition that affects how you can lie or breathe at night.
- You snore loudly, wake gasping, or have strong urges to move your legs at night.
- You're unsure when to start side sleeping in your pregnancy.
Call your doctor now if…
- Your baby is moving less than usual, the pattern changes, or you can't feel movement (call now, day or night; 911 if you can't reach anyone).
- You have vaginal bleeding or fluid leaking.
- You have a severe headache, vision changes, chest pain or trouble breathing (call your doctor or 911 now).
This page is general information, not medical advice. Every pregnancy and every child is different. Ask your doctor, midwife or pediatrician before changing supplements, diet or care.
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In the book: Chapter 14: Third Trimester: Getting Ready
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People also ask
Is the left side better than the right?
The UK MiNESS study found no difference between going to sleep on your left or right side. Either side is fine. Pick whichever is comfortable, and use a pillow behind your back to help you stay there.
What if I wake up on my back?
Don't panic. Just roll onto your side and go back to sleep. The research looked at the position women fell asleep in, because that's the position you hold longest. Nobody controls how they move once asleep.
When should I start sleeping on my side?
The UK advice is to go to sleep on your side from 28 weeks, at night and for naps. Ask your doctor or midwife if you're unsure when to start. Setting up your pillows a little earlier makes it feel normal by then.
Does this apply to naps?
Yes. The advice covers any time you go to sleep after 28 weeks, including daytime naps on the couch. Put a cushion behind your back so you stay on your side.