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Safe Sleeping Positions in Pregnancy: Why Left-Side Sleeping Matters

• Tim Kelas Antenatal & Postnatal
pregnancy sleep maternal-health

The short answer: after 28 weeks of pregnancy, the safest sleeping position is on your left side, because it maximises blood flow and oxygen to your baby. Sleeping flat on your back should be avoided, as it presses on the main vein that returns blood to your heart.

By the third trimester, sleep position is no longer just about comfort — it becomes a matter of fetal safety.

Why You Shouldn’t Sleep on Your Back

Lying flat on a horizontal surface (the supine position) after 28 weeks places the full weight of your uterus on the inferior vena cava (IVC), the main vein that carries blood back to your heart.

This pressure restricts a steady flow of oxygen to your baby and can trigger stillbirth if it continues for too long. That is why the back position should be avoided, especially during long stretches of sleep at night.

The Sleep-On-Side (Left) Position

Sleeping on your left side minimises pressure on your liver (which sits on your right side) and improves the capacity of the uterus-placenta blood supply. This makes it the preferred position for pregnant mothers.

Comfort Tips:

  • Place a maternity support pillow between your knees to take pressure off your hips.
  • Tuck another pillow behind your lower back to support your posture.
  • If you wake up on your back during the night, don’t panic — simply roll back onto your left side.
  • Left-side sleeping also helps reduce third-trimester heartburn — combine it with small, frequent meals for best results.
  • Mothers at high risk of high blood pressure in pregnancy are advised to sleep on their left side to support optimal blood circulation.

References

  • Cronin, R. S. et al. (2019). Maternal sleep position and stillbirth risk.

This article is for educational purposes and is not medical advice. Always consult your doctor or midwife.

Frequently Asked Questions

Why can't pregnant women sleep on their back after 28 weeks?

Lying flat on your back places the full weight of the uterus on the inferior vena cava (IVC), the main vein that returns blood to your heart. This pressure restricts the flow of oxygen to your baby and, if prolonged, can trigger stillbirth.

What is the safest sleeping position during pregnancy?

Sleeping on your left side (the sleep-on-side position) is the safest choice. It minimises pressure on your liver and improves the blood supply from the uterus to the placenta.

How can I sleep comfortably on my left side?

Use a maternity support pillow — place one between your knees and another behind your lower back to support your posture and stay comfortable through the night.

What are the risks of lying on my back for too long during pregnancy?

The weight of the uterus presses on the inferior vena cava (IVC), restricting a steady supply of oxygen to your baby. If this continues for too long, it can trigger stillbirth.