What position is safest to sleep in during pregnancy?

From 28 weeks (the third trimester), the safest thing is to go to sleep on your side — either side — for night-time sleep and daytime naps. Research (the UK MiNESS study) found that going to sleep on your back in late pregnancy is associated with around a 2.3 times higher risk of late stillbirth, because the weight of the bump can press on major blood vessels and reduce blood flow to the baby. This is general information — always follow your own midwife or GP's advice.

Does it have to be the left side?

Either side is the key message — both are far safer than your back. You may read that the left side is best, and one small study suggested a marginal benefit, but the main, well-evidenced advice from Tommy's is simply 'side, not back'. Sleep on whichever side is comfortable, and switch sides freely through the night.

What if I wake up on my back?

Don't panic. The advice is about the position you settle into to fall asleep — that's what the research measured. If you wake during the night or in the morning on your back, simply turn onto your side and go back to sleep. There's no need to lie awake checking your position. A pillow behind your back can help you stay on your side.

Do I really need a pregnancy pillow?

Not essential, but many people find one makes side-sleeping far more comfortable as the bump grows — and ordinary pillows between the knees and behind the back do much the same job for less. If you're buying one, match the shape to your main issue: a wedge for targeted bump or back support, a full-length or C-shape for general side-sleeping, or a U-shape if you want all-round support and help staying off your back.

When should I tell my midwife about sleep problems?

Mention any sleep issue at your routine appointments — it's very common and they'll have practical advice. See your midwife or GP sooner if you have severe or persistent heartburn, a strong urge to move your legs at night (restless legs, which can relate to low iron in pregnancy), significant pain, or if anxiety is badly affecting your sleep. Reduced or changed baby movements should always be reported straight away.

Pregnancy Sleep Guide: Positions, Pillows & Mattress

Sleep gets harder in pregnancy just as you need it most — between hormones, a growing bump and a long list of new aches, comfortable rest can feel out of reach. This guide walks through what changes in each trimester, the safe-sleep position advice that matters most, and the pillows and mattress set-up that genuinely help.

Written by Seán — Lead Reviewer, MattressReviews.ie

Testing team: Aoife (Side Sleeper Specialist), Ciarán (Back Sleeper Specialist), Siobhán (Combination Sleeper Specialist) & Oisín (Stomach Sleeper Specialist)

3+ years testing mattresses for Irish consumers. How we test · Meet the team

A note on health advice: This guide is for general information only and is not medical advice. Sleep problems can have many causes. If poor sleep is affecting your daily life, lasts more than a few weeks, or you suspect a condition such as insomnia or sleep apnoea, speak to your GP. In Ireland you can also find guidance at HSE.ie.

Your midwife comes first. Everything here is general information to help you sleep more comfortably. Pregnancy is individual, so your midwife, GP or obstetrician's advice always takes priority — and any reduced or changed baby movements should be reported to your maternity unit straight away.

Why pregnancy disrupts sleep

Broken sleep in pregnancy is the norm, not a sign anything is wrong — insomnia symptoms jump from around 6% before pregnancy to roughly 44% in the first trimester and over 60% by the third. Several things pile up at once:

Surging progesterone, which causes daytime drowsiness and night waking

Needing to wee more often as the uterus presses on the bladder

Nausea and breast tenderness early on

Heartburn and reflux as things shift and slow

A growing bump making any position hard to settle in

Leg cramps and restless legs, especially later on

Safe sleeping positions, trimester by trimester

First trimester (weeks 1–12)

Position isn't a safety concern yet, so sleep however is comfortable while you can. It's a good time to start getting used to side-sleeping, as it'll matter later — but there's no need to force it this early.

Second trimester (weeks 13–27)

Many people sleep best in this stretch as early nausea eases. As the bump grows, begin favouring your side and easing off back-sleeping, so that the third- trimester habit is already in place.

Third trimester (from 28 weeks) — the one that matters most

From 28 weeks, the advice is to go to sleep on your side — either side — for every sleep, including daytime naps. The UK MiNESS study found that settling to sleep on your back in late pregnancy is linked to around a 2.3 times higher risk of late stillbirth, because the weight of the bump can press on the large blood vessels behind it and reduce blood flow to your baby.

Two reassurances that matter: either side is fine (left or right — both are far safer than your back), and it's the position you fall asleep in that counts. If you wake on your back, don't panic — just turn onto your side and settle again. A pillow tucked behind your back helps you stay there.

Pregnancy pillow types & how to choose

A pregnancy pillow isn't essential — ordinary pillows between the knees and behind the back do much of the job — but the right one makes side-sleeping far more comfortable as the bump grows, and helps keep you off your back. Match the shape to your main need:

Wedge

Targeted support, small beds

A compact triangle that tucks under the bump, between the knees or behind the back. Cheapest and least intrusive; good for easing round-ligament or back strain and propping up for reflux.

Full-length body pillow

Side-sleeping & knee support

A long straight pillow to hug and drape a leg over, keeping the top hip from rotating. More support than a wedge, less bulk than a U or C shape.

C-shape

Back + bump in one

Curves around the body to cradle the head, bump and back, with the lower arm tucking between the knees. Good all-rounder that takes up less of the bed than a U.

U-shape

Full support, prevents rolling

Surrounds you on both sides — supporting head, bump, back and knees at once, and physically discouraging rolling onto your back. The most supportive, but it dominates the bed.

When choosing, think about fill (firmer memory foam holds its shape for support; fibre is softer, cooler and more mouldable but compresses over time) and look for a removable, washable cover — breathable cotton or bamboo sleeps cooler, which matters when pregnancy runs you warm. For everyday pillow support by sleep position, see our pillow guide.

Mattress considerations

Since you'll be spending the whole pregnancy on your side, your mattress matters more than usual. The aim is a surface that cushions the hip and shoulder so they don't ache under your weight, while still supporting your spine and the extra load of the bump — broadly a medium to medium-firm feel for most people.

•Too firm and the hip and shoulder take all the pressure on your side — a common cause of pregnancy hip pain.
•Too soft and you sink and lose support, making it harder to turn over (which you'll do a lot).
•Not ready to replace a mattress before a baby arrives? A good mattress topper can add pressure relief to a too-firm bed for far less.

Our best mattresses for side sleepers is the most relevant roundup, since you'll effectively be a side sleeper throughout.

Common issues — and what helps

Heartburn & reflux

Very common as pregnancy progresses. Sleeping on your left side and propping your upper body up slightly (a wedge pillow helps) reduces it, as does avoiding large or spicy meals close to bedtime. Persistent reflux is worth mentioning to your midwife or GP, who can advise on safe remedies.

Restless legs & cramps

Restless legs syndrome — an urge to move the legs at night — becomes more common as pregnancy goes on and can relate to low iron. Gentle stretching, keeping active by day and staying hydrated can help, but mention it to your midwife or GP, as they may check your iron levels.

Hip & pelvic pain

Pressure on the down-side hip and pelvic girdle pain make side-sleeping sore. A pillow between the knees keeps the hips and pelvis aligned, and a mattress or topper that cushions the hip takes the edge off. Pelvic pain that's limiting you is worth raising with your midwife, who can refer you to physiotherapy.

Find a mattress that's kind to side-sleeping

Comfortable side-sleeping for nine months comes down to the right pressure relief and support. Take our 2-minute quiz to be matched — no email required.

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Frequently Asked Questions

Keep reading

→ Best sleeping position: back vs side vs stomach — why side wins, and how to get comfortable.
→ Best mattresses for side sleepers — your position for the whole pregnancy.
→ Best pillows by sleep position — support beyond the bump.
→ Bedroom temperature for sleep — helpful if pregnancy is running you hot.

Sources

Tommy's — Sleep position in pregnancy (Sleep On Side) and the MiNESS research. View source
Tommy's — Sleeping position and stillbirth (MiNESS trial findings). View source
Johns Hopkins Medicine — Get a Good Night's Sleep During Pregnancy. View source