Quick Answer: The best sleeping position during pregnancy is on your left side (SOS, or "sleep on side"), especially in the second and third trimesters. Left-side sleeping maximises blood flow to the uterus, kidneys, and baby by keeping the weight of the uterus off the inferior vena cava (the large vein that returns blood from your lower body to your heart). A pillow between your knees and a supportive mattress make this position significantly more comfortable. According to the Sleep Foundation, left-side positioning during the second and third trimesters is widely recommended to support uterine and placental blood flow. Persistent positioning concerns should be raised with a prenatal provider.
Brad, Owner, 40+ years of experience: "We have been helping Brantford families sleep better since 1997. Every customer gets personal attention, honest advice, and the kind of follow-up service you just do not get from big box stores."
Sleep during pregnancy is one of those things nobody fully prepares you for. The first trimester, you are exhausted but cannot get comfortable. By the third trimester, every position feels wrong. Your back aches, your hips hurt, and the baby seems to kick hardest right when you are finally drifting off. Finding the right sleeping position is not just about comfort. It matters for blood flow, digestion, and reducing pressure on your growing body.
Related guides: why left-side sleeping matters in the third trimester, when a wedge pillow helps with reflux and hip pressure, and a broader guide to sleeping while pregnant. Visit our Brantford showroom if you want to test pregnancy pillows in person.
Reading Time: 8 minutes
Note: This article is for general information only. Always consult your healthcare provider about sleep positions specific to your pregnancy.
Why Left Side Sleeping Is Recommended
The Society of Obstetricians and Gynaecologists of Canada (SOGC) and most obstetric professionals recommend left-side sleeping during pregnancy. The reason is anatomical.
As the uterus grows, it becomes heavy enough to compress the inferior vena cava, the major vein running along the right side of your spine. When you lie on your back, this compression can reduce blood return to the heart, which means less blood flow to the placenta and baby. Lying on the left side shifts the uterus away from this vein.
That said, sleeping on your right side is also fine. The left-side preference is based on theoretical blood flow optimisation, and the difference between left and right is modest for most pregnancies. The important thing is to avoid prolonged back sleeping after about 20 weeks.
Can You Sleep on Your Back While Pregnant?
In the first trimester, sleeping on your back is generally safe. The uterus is still small and tucked inside your pelvis, so it is not pressing on anything important. The advice changes around the 20-week mark. By about week 20, roughly five months, the uterus is heavy enough that lying flat on your back can press it against two major blood vessels: the inferior vena cava, the large vein that returns blood from your lower body to your heart, and the aorta, the artery that carries blood out to your body and to the placenta. According to the Cleveland Clinic, that compression can reduce blood flow to your heart and to your baby.
Here is the reassuring part. Your body has its own warning system. If you spend too long flat on your back later in pregnancy, you may feel lightheaded, short of breath, or notice your heart beating faster. The Cleveland Clinic describes this as your body's way of telling you to roll onto your side. Short stretches on your back, even an hour or two, are not likely to cause lasting harm. The goal is simply to avoid spending the whole night flat on your back, not to panic over a few minutes.
What the Research Actually Says
You may have seen alarming headlines linking back sleeping to stillbirth, so here is the honest picture. An individual participant data meta-analysis led by Cronin and colleagues, published in EClinicalMedicine in 2019, found that going to sleep in the supine (back) position in late pregnancy was associated with higher odds of late stillbirth, with an adjusted odds ratio of 2.63 and a population attributable risk of 5.8%. In plain terms, that study estimated that if no one went to sleep on their back in late pregnancy, late stillbirths might fall by roughly that amount. Just as importantly, a large prospective study funded by the U.S. National Institutes of Health, through its NICHD nuMoM2b study (2019), found that going to sleep on the back or right side during early and mid pregnancy was not associated with an increased risk of stillbirth, a small-for-gestational-age baby, or high blood pressure disorders. The picture most providers settle on: the caution is about the going-to-sleep position in late pregnancy, the evidence is reassuring for early and mid pregnancy, and you should not lie awake worrying about the position you happen to wake up in. Always follow your own prenatal provider's guidance.
Talia Grose, sleep specialist, Mattress Miracle: "Almost every back sleeper who comes in pregnant asks me the same question: how am I supposed to fall asleep on my side when I have slept on my back my whole life? My honest answer is that you train the bed, not yourself. Put a firm pillow along your back so that if you drift onto it in your sleep, you settle on a gentle incline instead of going completely flat. Tuck a pillow between your knees so your hips stop aching and the side position actually feels good enough to stay in. And please do not lie there policing yourself all night. If you wake up on your back, just roll over and go back to sleep. The position you fall asleep in matters far more than the one you wake up in."
If You Are a Habitual Back Sleeper: How to Make the Switch
- Build an incline with a pillow behind your back: Wedge a firm pillow or a folded blanket along your back so that if you roll over in your sleep, you land on a gentle 20 to 30 degree tilt rather than flat. The Cleveland Clinic notes that even a 20 to 30 degree angle takes the pressure off the inferior vena cava. A wedge pillow does the same job with less rearranging.
- Use a knee pillow to make side sleeping comfortable: The reason back sleepers keep rolling onto their backs is usually hip and lower-back ache. A pillow between the knees keeps the pelvis aligned and eases that ache, so your body stops fighting the side position.
- Do not panic if you wake up on your back: This is the single most important point. Drifting onto your back for part of the night will not harm your baby. Just roll to your side, ideally the left, and carry on. Guilt and 3 a.m. anxiety cost you far more sleep than the position ever will.
- Give it a couple of weeks: Most lifelong back sleepers tell us their bodies adjust within two to three weeks, especially once the belly is big enough that side sleeping simply feels better.
Sleeping Position by Trimester
First Trimester (Weeks 1-12)
The good news: any sleeping position is generally safe during the first trimester. The uterus is still small and within the pelvis. The bad news: fatigue and nausea can make sleep difficult regardless of position. If nausea is worse when lying down, try elevating your upper body slightly with an extra pillow or an adjustable bed base.
Second Trimester (Weeks 13-27)
This is when side sleeping becomes more important. The uterus is growing above the pelvis, and back sleeping may start to feel uncomfortable. Many women naturally shift to side sleeping during this period. A pillow between the knees reduces hip and lower back strain.
Third Trimester (Weeks 28-40)
Side sleeping is strongly recommended now. The uterus is at its heaviest, and the vena cava compression risk is real. You will likely need more pillow support: between the knees, under the belly, and possibly behind your back to prevent rolling over. A mattress that contours to your body without creating pressure points becomes genuinely important at this stage.
Mattress Support During Pregnancy
Pregnancy changes your body's relationship with your mattress. Weight increases, your centre of gravity shifts, and pressure points at the hips and shoulders intensify, especially for side sleepers.
Dorothy, who coordinates our Brantford showroom, works with expecting mothers regularly: "The most common complaint I hear is hip pain. When you sleep on your side with a growing belly, all that extra weight concentrates at the hip. If the mattress is too firm, it pushes back against the hip bone. If it is too soft, the hip sinks and the spine curves. What you need is something that cradles the hip while supporting everything else."
A mattress with individually wrapped pocket coils does this well because each coil adjusts independently to the weight above it. The coils under your hip compress more while the coils under your waist provide support. Our Restonic ComfortCare Queen with 1,222 individually wrapped coils at $1,619 is a strong option for this reason. Each coil responds to your body's specific pressure profile.
For women who find even a good mattress is not enough in the third trimester, a mattress topper can add a temporary layer of pressure relief without replacing the entire mattress. Choose one that is 2 to 3 inches thick with memory foam or latex for the most contouring.
Firmness Guide for Pregnancy
If you weigh under 150 lbs pre-pregnancy, a plush mattress (4-5 firmness) usually provides enough contouring for side sleeping. Between 150 and 200 lbs, medium (5-6) is typically ideal. Over 200 lbs, a medium-firm (6-7) prevents excessive sinking while still offering pressure relief. These are general guidelines. Every body is different, which is why we encourage trying mattresses in person at our Brantford showroom.
Pillow Strategies That Actually Help
- Between the knees: Keeps the pelvis aligned and reduces strain on the hips and lower back. This is the single most effective pillow placement during pregnancy.
- Under the belly: A thin pillow or folded towel under your belly takes weight off the side you are lying on and reduces pull on your back muscles.
- Behind your back: Prevents you from rolling onto your back during the night. A regular bed pillow works fine for this.
- Under your head: Your regular pillow, but consider whether it is thick enough for side sleeping. The gap between your ear and the mattress surface needs to be filled to keep your neck aligned.
- Full-body pregnancy pillows: C-shaped or U-shaped pregnancy pillows combine several of these functions into one. They are bulky but effective, especially in the third trimester.
Visiting Our Showroom While Pregnant
We genuinely encourage expecting mothers to visit our Brantford showroom at 441 1/2 West Street and lie on mattresses in their actual side-sleeping position. Bring your favourite pillow. Spend 10 to 15 minutes in the position you actually sleep in. Your body will tell you immediately whether the firmness is right. Dorothy works with pregnant customers regularly and understands the specific support needs at each stage.
Find Your Perfect Mattress at Mattress Miracle
We are a family-owned mattress store in Brantford, helping our community sleep better since 1997. Come try mattresses in person and get honest, no-pressure advice.
441 1/2 West Street, Brantford, Ontario
Call 519-770-0001Frequently Asked Questions
Can I sleep on my back while pregnant?
In the first trimester, generally yes. After about 20 weeks, most healthcare providers suggest avoiding long stretches flat on your back, because the weight of the uterus can compress the inferior vena cava and aorta and reduce blood flow to the placenta. You do not have to sleep sitting up. Propping yourself on a 20 to 30 degree incline with a pillow relieves most of the pressure. Reassuringly, NIH-funded research found no increased risk from back or right-side sleep in early and mid pregnancy, so if you wake up on your back, do not panic, just roll to your side. Consult your doctor for advice specific to your pregnancy.
How do I stop sleeping on my back while pregnant?
Make side sleeping the easier option. Put a firm pillow behind your back so you settle onto a gentle incline if you roll over, and tuck a pillow between your knees so your hips stop aching and the side position feels comfortable enough to stay in. A wedge pillow works well too. Most lifelong back sleepers adjust within two to three weeks. If you do wake on your back, simply roll over, short periods do no harm.
Is it okay to sleep on my right side during pregnancy?
Yes. While left-side sleeping is theoretically optimal for blood flow, sleeping on your right side is also safe and far better than sleeping on your back in later trimesters. The most important thing is to avoid prolonged back sleeping after 20 weeks. Do not stress about which side you wake up on.
What mattress firmness is best for pregnancy?
Medium to medium-plush (5-6 on a 10-point scale) works for most pregnant women who are side sleeping. You need enough give to cushion the hip and shoulder without so much sinking that the spine curves. A mattress with individually wrapped coils, like our Restonic ComfortCare with 1,222 coils, adjusts to your body's specific pressure points. Visit us at 441 1/2 West Street to test in person.
Do I need a pregnancy pillow?
Not necessarily. Many women do fine with regular pillows arranged strategically: one between the knees, one under the belly, one behind the back. A dedicated pregnancy pillow (C-shape or U-shape) is more convenient but takes up significant bed space. Try the individual pillow approach first and upgrade if needed.
Can an adjustable bed help during pregnancy?
Yes, particularly for women with nausea, acid reflux, or shortness of breath. Elevating the upper body reduces reflux symptoms and makes breathing easier as the baby grows. Our adjustable bed bases work with most mattresses and can be a worthwhile investment that continues to be useful long after pregnancy. Call (519) 770-0001 to ask about options.
Visit Our Brantford Showroom
Mattress Miracle
441 1/2 West Street, Brantford
Phone: (519) 770-0001
Hours: Mon-Wed 10-6, Thu-Fri 10-7, Sat 10-5, Sun 12-4
Our team has 40+ years of experience in the mattress industry, helping customers find the right sleep solution. Call ahead or walk in any day of the week.
Visit Our Brantford Showroom
We are located at 441½ West Street in downtown Brantford. Free parking available. Our team does not work on commission, so you get honest advice based on your needs.
Mattress Miracle , 441½ West Street, Brantford, ON · (519) 770-0001
Hours: Monday–Wednesday 10am–6pm, Thursday–Friday 10am–7pm, Saturday 10am–5pm, Sunday 12pm–4pm.
Sources
- Cleveland Clinic. "Why Do They Say Not To Sleep on Your Back When You're Pregnant?" health.clevelandclinic.org
- Sleep Foundation. "Pregnancy Sleeping Positions." sleepfoundation.org
- Cronin RS, Li M, Thompson JMD, et al. "An Individual Participant Data Meta-analysis of Maternal Going-to-Sleep Position, Interactions with Fetal Vulnerability, and the Risk of Late Stillbirth." EClinicalMedicine, 2019. PubMed 31193832
- Silver RM, Hunter S, Reddy UM, et al. (nuMoM2b study). "Maternal Sleep Position and Adverse Pregnancy Outcomes." 2019. NIH/NICHD-funded. nichd.nih.gov