Why is sleeping on the left side recommended during pregnancy?

Left Side Sleeping During Pregnancy: Benefits and Recommendations

Sleeping on the left side during pregnancy is recommended because it optimizes maternal hemodynamics, improves placental blood flow, and reduces the risk of aortocaval compression, which can lead to decreased oxygen delivery to the fetus. 1, 2

Physiological Basis for Left Side Sleeping

• Aortocaval Compression Prevention: When a pregnant woman lies supine (on her back), the gravid uterus can compress the inferior vena cava and aorta, leading to:

  • Decreased venous return to the heart
  • Reduced cardiac output
  • Decreased placental perfusion
  • Potential maternal hypotension ("supine hypotension syndrome")

• Improved Placental Blood Flow: MRI studies have shown that compared to the supine position, the left lateral position in late pregnancy is associated with:

  • 23.7% higher internal iliac arterial blood flow to the uterus
  • 6.2% greater oxygen movement across the placenta
  • Improved fetal oxygen delivery and umbilical venous blood flow 2

Clinical Evidence Supporting Left Side Sleeping

Research has demonstrated that maternal position significantly affects maternal-fetal hemodynamics:

• A 2021 MRI study found that the supine position in late pregnancy reduced utero-placental blood flow and oxygen transfer across the placenta compared to the left lateral position 2

• Observational studies show that pregnant women naturally tend to adopt left-sided sleeping positions in late pregnancy, with 77% of women beyond 30 weeks gestation adopting a left tilt during sleep compared to only 26% of non-pregnant controls 3

• Studies monitoring maternal and fetal heart rates during sleep found that left side sleeping was associated with lower maternal heart rate and higher heart rate variability compared to right side or supine positions 4

Clinical Recommendations

• Optimal Position: Left lateral position is preferred during sleep and for extended periods of rest during pregnancy, especially after 20 weeks gestation

• During Medical Procedures: For pregnant patients undergoing surgical or endoscopic procedures:

  • The left lateral tilt position is advised to maintain hemodynamic stability
  • This position minimizes aortocaval compression and maintains cardiac return
  • More vasoactive medications are needed to maintain hemodynamic stability when patients are not in left lateral tilt position 1

• After 20 Weeks: Pregnant women should not lie supine for extended periods, including during endoscopic or surgical procedures 1

Common Misconceptions and Pitfalls

• Not All Side Sleeping Is Equal: While both left and right side sleeping are better than supine, left side is optimal for maximizing blood flow to the placenta

• Intermittent Position Changes: Brief periods in other positions are acceptable, but extended time in the supine position should be avoided, especially in late pregnancy

• Individual Comfort: Some women may naturally avoid positions that cause discomfort due to pre-syncopal symptoms, but even asymptomatic women should be advised to sleep on their left side 5

• Inconsistent Advice: Despite evidence supporting left side sleeping, some healthcare providers may not emphasize its importance, leading to confusion for pregnant women

Special Considerations

• High-Risk Pregnancies: Left side sleeping may be particularly important for women with:

  • Hypertensive disorders of pregnancy
  • Intrauterine growth restriction
  • Placental insufficiency

• Interventions: Positional therapy devices designed to reduce supine sleeping in pregnancy have shown promising results in reducing time spent supine and improving both maternal oxygen saturation and fetal heart rate patterns 6

By following these recommendations for left side sleeping during pregnancy, women can optimize blood flow to the placenta and potentially improve maternal-fetal outcomes.