What is the best sleep position for a mother in her 2nd trimester?

Best Sleep Position During Second Trimester of Pregnancy

The left lateral position is the recommended sleep position for pregnant women in their second trimester as it optimizes maternal cardiac output, improves utero-placental blood flow, and enhances oxygen delivery to the fetus. 1, 2

Physiological Rationale for Left Lateral Position

• Hemodynamic Benefits:

  • In the second trimester, the enlarging uterus begins to compress the inferior vena cava when lying supine, starting around 12 weeks of gestational age 1
  • MRI studies show that at 20 weeks of gestation, the left lateral position significantly increases:
    • Ejection fraction by 8%
    • Stroke volume by 27% 1
  • By 32 weeks, these benefits become even more pronounced with:
    • 11% increase in ejection fraction
    • 21% increase in end-diastolic volume
    • 35% increase in stroke volume
    • 24% increase in cardiac output 1

• Reduced Risk of Vena Cava Compression:

  • The supine position causes significant compression of the inferior vena cava by the gravid uterus 3
  • This compression results in:
    • 16.4% reduction in cardiac output
    • 85.3% reduction in blood flow through the IVC at its origin
    • 44.4% reduction in blood flow at the level of the renal veins 3

Impact on Placental Blood Flow and Fetal Oxygenation

• Improved Utero-Placental Circulation:

  • Supine positioning causes a 23.7% reduction in total internal iliac arterial blood flow to the uterus 2
  • Left lateral positioning enhances placental oxygen transfer by approximately 6.2% compared to supine position 2
  • Studies show that maternal supine position reduces fetal umbilical venous blood flow by about 11% 2

• Clinical Implications:

  • Most clinicians recommend avoiding the supine horizontal position, especially during the second and third trimesters 1
  • This minimizes pressure from the gravid uterus on the inferior vena cava, which can decrease venous return and cardiac output 1

Practical Recommendations

• Optimal Sleep Positions:

  • Left lateral position is most beneficial 1, 2
  • Right lateral position is acceptable but not as optimal as left lateral 4
  • Avoid supine (back) position when possible 1, 3

• Sleep Environment Modifications:

  • Use pillows to support the body in the left lateral position
  • Consider placing a pillow between the knees to reduce pressure on the lower back
  • If experiencing reflux (common in pregnancy), timing physiotherapy and meals appropriately may help 1

Special Considerations

• For Women with Specific Conditions:
  • Women with high-risk pregnancies or fetal growth restriction should be particularly vigilant about avoiding the supine position, as research shows an additive negative effect on fetal oxygenation 5
  • For women experiencing preterm labor, the left lateral position has been shown to significantly reduce the frequency of uterine contractions compared to the supine position 6

Practical Tip

• Interestingly, sleeping on the left-hand side of the bed is associated with maintaining a left-side sleeping position throughout the night 7, so this simple adjustment to sleeping arrangements may help maintain the optimal position.

By prioritizing left lateral sleeping position during the second trimester, pregnant women can optimize blood flow to the placenta and fetus, potentially reducing risks associated with reduced cardiac output and placental perfusion.