Quick Answer: Pregnancy insomnia is extremely common , affecting up to 78% of pregnant people, most severely in the third trimester. The main causes are physical discomfort, frequent urination, heartburn, leg cramps, and anxiety. Left side sleeping on a firm-but-comfortable mattress with strategic pillow support is the most evidence-backed position for third-trimester comfort and fetal circulation. Most sleep aids are not safe in pregnancy , always check with your midwife or OB before taking anything.
In This Guide
Reading Time: 8 minutes
Medical disclaimer: This article provides general information about sleep during pregnancy and is not a substitute for guidance from your obstetrician, midwife, or healthcare provider. Always consult your healthcare provider before making changes to medications, supplements, or sleep aids during pregnancy.
How Common Is Pregnancy Insomnia?
Very common. A 2023 systematic review in the journal Sleep Medicine Reviews (Mindell et al.) found that sleep disturbance affects between 46% and 78% of pregnant people, with the prevalence increasing in each trimester. By the third trimester, fewer than 30% of pregnant people report sleeping well without significant disruption.
This is not primarily a psychological phenomenon , it's largely physical. The body undergoes profound changes that directly affect sleep: hormonal shifts, physical growth, increased metabolic demand, and displacement of internal organs all contribute independently. Understanding the specific cause at each stage helps identify the most effective responses.
Why Pregnancy Disrupts Sleep: The Physiology
Progesterone, which rises significantly in the first trimester, has a sedating effect but also causes more frequent urination and nasal congestion. Oestrogen fluctuations affect REM sleep architecture. By the third trimester, the uterus presses on the vena cava (the large vein returning blood to the heart) when lying on the right side or back, reducing cardiac output and potentially affecting fetal blood flow. The Society of Obstetricians and Gynaecologists of Canada (SOGC) recommends left side sleeping from 28 weeks onward for this reason.
8 min read
Causes by Trimester
| Trimester | Main Sleep Disruptors | Notes |
|---|---|---|
| First (weeks 1–12) | Frequent urination, nausea, breast tenderness, fatigue, anxiety | Daytime fatigue often severe; difficulty maintaining comfortable position as breast sensitivity increases |
| Second (weeks 13–26) | Leg cramps, vivid dreams, round ligament pain, heartburn beginning | Often the best sleep trimester; fetal movement begins and can interrupt sleep |
| Third (weeks 27–40) | Back pain, fetal movement, heartburn/GERD, difficulty breathing (diaphragm compressed), leg cramps, pelvic discomfort, anxiety about labour | Most severe sleep disruption; average of 3–4 night wakings common by week 36 |
Best Sleep Position in Pregnancy
Left Side Sleeping: The Evidence-Backed Recommendation
The Society of Obstetricians and Gynaecologists of Canada and most major obstetric bodies recommend sleeping on the left side from the third trimester. The left lateral position keeps the uterus off the vena cava (which runs along the right side of the spine), optimises blood flow to the placenta, and reduces pressure on the liver.
A large 2019 prospective study in The Lancet (Stacey et al.) found that going to sleep on the back in the third trimester was associated with a 2.3-fold increased risk of late stillbirth compared with going to sleep on the left side. The mechanism is thought to involve compression of the vena cava and aorta. Waking up on your back is not harmful , what matters is the position you fall asleep in.
If Left Side Sleeping Is Uncomfortable
Many people find left side sleeping uncomfortable initially, particularly if they're right-side sleepers by habit. Strategies that help:
- A full-length body pillow between the knees, under the belly, and at the back prevents rolling and supports the growing bump
- A dedicated pregnancy pillow (C-shaped or U-shaped) provides wrap-around support in one product
- A small pillow under the hip can relieve hip joint pressure on bony-hipped sleepers
- Right side sleeping is still significantly safer than back sleeping , if left side becomes genuinely unbearable, right side is acceptable
What About Back Sleeping?
Back sleeping (supine) is comfortable in the first and second trimesters for most people. From 28 weeks, it's recommended to avoid falling asleep on the back. If you wake up on your back, simply roll to your left , there's no need for alarm about having rolled during sleep.
Mattress and Pillow Tips
Your mattress becomes significantly more important during pregnancy, particularly in the third trimester when finding a comfortable position requires more effort.
What to Look For in a Pregnancy-Friendly Mattress
- Pressure relief at the hips and shoulders: Side sleeping throughout the night puts sustained pressure on the hip and shoulder that's in contact with the mattress. A medium to medium-firm mattress with a comfort layer that contours gently , rather than a very firm, flat surface , reduces this pressure significantly.
- Spinal support: As the abdomen grows, the centre of gravity shifts and lumbar lordosis (lower back curve) increases. A mattress that sags in the middle exacerbates back pain; one that maintains a neutral spine alignment helps.
- Temperature regulation: Many pregnant people experience increased body temperature, particularly in the third trimester. A mattress with cooling properties , natural latex, innerspring with good airflow, or a foam with gel infusion , reduces night sweating.
- Edge support: Getting in and out of bed becomes harder as pregnancy progresses. A mattress with firm edge support makes this easier and safer.
Dorothy, Sleep Specialist: "We've helped quite a few expectant parents choose mattresses over the years. The conversation usually comes down to: they need something with enough give to relieve hip pressure in side sleeping, but still supportive enough that they don't sink and create a V-shape in the spine. A medium-firm innerspring or hybrid usually hits both. The Restonic ComfortCare Queen is often exactly what people need in this situation."
Pillow Support During Pregnancy
A single bed pillow is rarely enough by the third trimester. Common pillow arrangements for pregnant side sleepers:
- One pillow under the head (appropriate loft for shoulder width)
- One long pillow or body pillow hugged in front, between the knees, and supporting the belly
- One small pillow or rolled towel at the lower back for lumbar support
Pregnancy-specific pillow designs (U-shaped, C-shaped, or full-length body pillows) integrate these functions into one product. They take up significant bed space but can be transformative for comfort after 30 weeks.
Safe Remedies for Pregnancy Insomnia
Most sleep aids , including most antihistamine-based over-the-counter sleep tablets, herbal supplements, and prescription sedatives , have not been adequately studied in pregnancy and are generally not recommended. Here are approaches with better safety profiles.
Evidence-Supported Approaches
- Cognitive Behavioural Therapy for Insomnia (CBT-I): The most effective non-pharmacological treatment for insomnia in any population, including pregnancy. Involves sleep restriction, stimulus control, and addressing anxiety around sleep. Available through psychology referrals and increasingly through digital platforms (e.g., Sleepio). A 2020 study in Sleep Medicine confirmed CBT-I effectiveness during pregnancy.
- Consistent sleep schedule: Same wake time every day, including weekends, anchors the circadian rhythm. This is the single most impactful behavioural intervention for insomnia.
- Cool bedroom (18–20°C): Particularly important in pregnancy when body temperature is elevated.
- Reducing liquid intake after 6 p.m.: Reduces night-time urination without affecting daily hydration needs (drink the bulk of fluids before dinner).
- Elevation for heartburn: Raising the head of the bed by 15–20 cm (using bed risers or a wedge pillow) significantly reduces GERD symptoms that wake pregnant people in the second and third trimester.
- Stretching before bed: Gentle calf stretches and hip flexor stretches before sleep reduce the frequency of leg cramps, a common third-trimester disruptor.
Melatonin in Pregnancy
Melatonin is commonly used in non-pregnant adults and widely available in Canada. However, the Society of Obstetricians and Gynaecologists of Canada does not currently recommend melatonin during pregnancy due to insufficient safety data. Melatonin crosses the placenta and may affect fetal circadian rhythm development. Discuss with your OB or midwife before use.
What to Avoid
- Over-the-counter sleep aids (diphenhydramine/Benadryl, doxylamine used alone for sleep): While doxylamine is sometimes used for nausea in pregnancy, sleep-dose antihistamines should only be used with medical guidance during pregnancy.
- Herbal sleep supplements (valerian, kava, passionflower, chamomile in large amounts): Inadequate safety data for pregnancy.
- Caffeine after midday: SOGC recommends limiting caffeine to 200 mg/day during pregnancy (roughly one medium coffee). Caffeine has a longer half-life in pregnancy and will significantly affect sleep if consumed after noon.
- Alcohol: No safe level in pregnancy, and alcohol disrupts sleep architecture even in non-pregnant adults.
- Extended screen use before bed: Blue light exposure suppresses melatonin; this effect is not reduced by pregnancy.
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Is it safe to take melatonin during pregnancy?
The Society of Obstetricians and Gynaecologists of Canada does not currently recommend melatonin during pregnancy due to insufficient evidence of safety. Melatonin crosses the placenta and may affect fetal development. Discuss with your OB or midwife before use. Non-pharmacological approaches (consistent schedule, cool room, CBT-I) are the recommended first line.
Is insomnia during pregnancy harmful to the baby?
Occasional poor sleep during pregnancy is not harmful to the fetus. Chronic severe sleep deprivation may be associated with increased risk of preterm labour and prolonged labour duration, according to a 2010 study in the American Journal of Obstetrics and Gynecology (Lee et al.). This is one reason addressing insomnia proactively , through behavioural approaches and position optimisation , is worthwhile rather than simply enduring it.
What if I can't sleep on my left side?
Right side sleeping is acceptable and significantly safer than back sleeping in the third trimester. If left side sleeping causes hip pain, a body pillow between the knees and a small pillow under the belly usually resolves this. If a mattress is causing significant hip pressure on the side, a medium-soft topper (2–3 inches of latex or memory foam) adds contouring without completely changing the support layer.
Why do I have vivid dreams in pregnancy?
Vivid dreams are extremely common during pregnancy, particularly in the first and third trimesters. The mechanism isn't fully established, but hormonal changes (particularly progesterone) affect REM sleep quality and intensity. Increased night wakings , common in pregnancy , also mean you're more likely to remember dreams, since dream recall is strongest when waking directly from REM sleep.
Will a new mattress help with pregnancy insomnia?
If your current mattress is contributing to hip pain, shoulder pressure, or poor spinal alignment in side sleeping, a mattress better suited to side sleeping can make a genuine difference to sleep quality. A medium to medium-firm mattress with good pressure relief at the hips and consistent support is the target. The benefit is most pronounced in the third trimester when sustained side sleeping creates the most pressure-point issues.
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