Sleeping on your left side is the most recommended position throughout pregnancy. It improves blood circulation to the placenta, reduces pressure on the inferior vena cava (the large vein running along your right spine), and supports kidney function. From the second trimester onwards, back sleeping and stomach sleeping should be avoided. If you wake up on your back, simply turn onto your side. There is no need to panic.
In our article, we cover what to do trimester by trimester, which positions to avoid and why, and what you can do with pillows and your sleep setup to stay comfortable as your body changes. If you have pre-existing health conditions that impact your rest, it's always a good idea to consult targeted advice for your specific situation.
Why Sleeping Position Matters During Pregnancy
Sleep is one of the most important things you can do for your health during pregnancy. It is when your body repairs tissue, regulates hormones, and supports fetal development. However, as your pregnancy progresses, the way you sleep starts to matter in ways it simply did not before.
The growing uterus adds significant weight and shifts your centre of gravity. From around the 20-week mark, lying flat on your back causes the uterus to press against the inferior vena cava, which can reduce blood flow returning to your heart and, in turn, reduce oxygen and nutrient delivery to the baby. Research published in BMC Pregnancy and Childbirth found that around 78% of pregnant women experience back pain, and sleeping position is a key contributing factor.
Poor sleep posture during pregnancy is also associated with increased risk of heartburn, swelling in the legs and feet, shortness of breath, and disturbed sleep quality overall. The good news is that adjusting your position, even in small ways, can make a meaningful difference.
Sleeping Positions by Trimester: What Changes and When
First Trimester (Weeks 1 to 13)
In the first trimester, your uterus is still relatively small and well protected within the pelvis. At this stage, you can generally sleep in whatever position feels most comfortable, including on your back or stomach if that is your natural preference.
That said, starting to sleep on your side early in pregnancy is worth practicing. Building the habit now means the transition will feel natural rather than disruptive when it becomes more important in the second trimester. Nausea, frequent urination, and breast tenderness are more likely to disrupt sleep at this stage than the position itself.
Second Trimester (Weeks 14 to 27)
This is the trimester where sleeping position starts to matter more directly. As the uterus grows beyond the pelvis and begins to sit above the waistline, sleeping on your back puts increasing pressure on the vena cava. Most obstetric guidance recommends transitioning away from back sleeping by around 20 weeks.
This trimester also tends to be when hip and lower back discomfort start. Placing a pillow between your knees keeps your hips in neutral alignment and significantly reduces pressure on the lower back. A supportive pregnancy pillow can also help prop and cushion the belly as it grows.
Third Trimester (Weeks 28 to 40)
By the third trimester, back sleeping should be avoided entirely due to peak pressure on the vena cava, making side sleeping with robust pillow support the standard recommendation. Many women find they need multiple pillows to maintain alignment, including one between the knees, one under the belly, and one behind the back to prevent rolling.
If you experience shortness of breath or heartburn, slightly elevating your upper body can relieve the pressure the uterus places on your diaphragm and stomach. Choosing the right mattress for a comfortable pregnancy is worth addressing before the third trimester if possible. A mattress that is too soft can cause the hips to sink, throwing the spine out of alignment. One that is too firm can create uncomfortable pressure points on the hips and shoulders.
The Best Sleeping Position for Pregnant Women: Left Side Explained
Left-side sleeping is recommended by most obstetric guidelines and for good reason. Here is what it actually does for your body:
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Improves circulation
Sleeping on the left side keeps the uterus from pressing against the vena cava, the large vein on the right side of the spine that carries blood from the lower body back to the heart. This supports better blood flow to the placenta.
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Reduces swelling
Left-side sleeping supports kidney function, which helps process waste and excess fluid more efficiently. This can reduce swelling in the hands, feet, and ankles that is common in later pregnancy.
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Relieves back pressure
The position reduces load on the lumbar spine, which already bears extra strain from the shifting centre of gravity during pregnancy.
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Supports nutrient delivery
Blood flow to the placenta means better oxygen and nutrient supply to the baby throughout the night.
That said, staying on one side all night is neither realistic nor necessary. Right-side sleeping is also safe. If you wake up on your back in the night, simply shift back onto your side. Waking up in a different position does not mean harm has been done. The guidance around left-side sleeping is about reducing cumulative pressure over time, not about avoiding a single instance of rolling over.
Is Right-Side Sleeping Safe During Pregnancy?
Yes. Right-side sleeping is considered safe throughout pregnancy. While left-sided sleeping is theoretically better for vena cava blood flow, the difference is not clinically significant enough to cause concern if you naturally prefer the right side or find yourself switching during the night.
The more important thing is to avoid back sleeping from the second trimester onwards. Between the left and right side, comfort should be your guide. If one side causes hip discomfort, numbness, or joint ache, switch sides. Alternating sides throughout the night is fine and may reduce pressure buildup on a single hip.
Sleeping Positions to Avoid During Pregnancy
Back Sleeping (Supine Position)
Lying flat on your back places the full weight of the uterus directly on the inferior vena cava and the aorta. From around 20 weeks, this can reduce blood flow to the heart, cause a drop in blood pressure, and decrease the supply of oxygen and nutrients reaching the baby. Symptoms can include dizziness, shortness of breath, and nausea.
Research indicates that up to 15% of pregnant women experience a form of supine hypotensive syndrome as a direct result of back sleeping in later pregnancy. Beyond circulation, back sleeping in the third trimester also increases spinal compression and can worsen back pain significantly.
Stomach Sleeping
Stomach sleeping is naturally uncomfortable to maintain as the belly grows and most women shift away from it organically by around the 16-to-18-week mark. As the uterus expands, the pressure this position creates on the abdomen becomes impractical and potentially unsafe.
If you’re a habitual stomach sleeper and find the transition difficult, a pillow placed under your hip or pelvis (rather than your belly) can make side sleeping feel slightly closer to what your body is used to.
How to Use Pillows to Stay Comfortable Through the Night
Pillow placement is one of the most practical and underrated tools for managing sleep comfort during pregnancy. The right setup reduces pressure, maintains spinal alignment, and supports the belly, so you’re not fighting your own weight throughout the night. Make sure to opt for supportive pillows suited to pregnancy and general sleep support.
Here are the most effective positions:
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Between the knees: Place a standard pillow between your knees when lying on your side. This keeps the pelvis neutral and takes pressure off the hips and lower back. This single adjustment alone makes a significant difference for most women from the second trimester onwards.
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Under the belly: A rolled towel or small pillow placed under the belly provides lift and reduces the pulling sensation that can develop in the lower abdomen as the belly grows heavier.
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Behind the back: Placing a pillow behind your back prevents you from rolling backward onto your spine during the night. It acts as a passive barrier without requiring you to stay consciously positioned.
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Elevating the upper body: For heartburn and breathing difficulty, propping yourself up at a 30-to-45-degree angle with stacked pillows or a wedge pillow can provide real relief, especially in the third trimester.
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Full-length body pillow: A U-shaped or C-shaped pregnancy pillow does most of the above simultaneously. They are bulky but genuinely useful from the second trimester onwards if you tend to move around a lot during sleep.
Your Mattress Matters: What to Look for During Pregnancy
Position and pillow placement can only do so much if the surface you sleep on does not support your body properly. During pregnancy, mattress performance becomes more important than it typically would be because your weight distribution shifts every few weeks and pressure-point sensitivity increases, particularly at the hips and shoulders.
A mattress that is too soft allows the hips to sink, creating a misaligned curve in the spine that contributes to lower back pain. A mattress that is too firm creates concentrated pressure at the hip and shoulder contact points, causing discomfort in the side-sleeping position that pregnancy requires. The ideal mattress for pregnancy offers zoned or adaptive support: slightly softer at the shoulders and hips, firmer at the core to keep the spine neutral.
That said, it’s important to look for a supportive sleep system that gently stretches and decompresses the spine during sleep. For pregnant women dealing with back tension and postural strain, the principle of alignment support during sleep is particularly relevant.
Additional Tips for Better Sleep During Pregnancy
Sleeping position is the foundation, but it is rarely the only factor affecting your rest. These habits work alongside good positioning to improve overall sleep quality:
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Limit fluids before bed
Reducing how much you drink in the hour or two before sleep cuts down on night-time trips to the bathroom, which are already more frequent during pregnancy due to increased kidney activity and bladder pressure.
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Keep the room cool
Body temperature rises during pregnancy due to increased blood volume and metabolic activity. A cooler room, around 18 to 20 degrees Celsius, supports the natural drop in core temperature needed for sleep onset.
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Wind down consistently
A predictable pre-sleep routine signals to the body that rest is approaching. Avoiding screens, dimming lights, and reducing stimulation for 30 to 60 minutes before bed can help you fall asleep faster and more easily.
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Sleep on your left if you have heartburn
Lying on your left side keeps the stomach below the esophagus, which helps reduce acid reflux. This is one of the more immediate, practical benefits of left-side sleeping beyond circulation.
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Address hip pain early
If you are developing hip discomfort from side sleeping, address it early with a pillow between your knees and, if needed, a mattress topper to add surface cushioning. Hip pain tends to worsen throughout the trimester if left unaddressed.
Rest Comfortably Through Every Stage of Pregnancy
Getting quality sleep during pregnancy comes down to three things: the right position, the right support, and a setup that adapts as your body changes. Left-side sleeping is your best default from the second trimester onwards, a pillow between the knees reduces hip and back pressure more than most people expect, and a mattress that holds the spine in neutral alignment makes both easier to sustain through the night.
If you’re finding sleep increasingly difficult as your pregnancy progresses, the most effective changes are usually the simplest ones: adjust your position, add a pillow, and make sure your sleep surface is actually working with your body rather than against it.
