What best describes systemic vascular resistance during pregnancy?

What best describes systemic vascular resistance during pregnancy?

• A. Increases 20 to 30%, remaining elevated
• B. Decreases 20 to 30%, with the lowest values at 14 to 24 weeks and returning to pre-pregnancy by term
• C. Remains unchanged throughout pregnancy
• D. Fluctuates unpredictably with no clear pattern

Answer: (B)

Systemic vascular resistance falls during pregnancy due to widespread vasodilation driven by hormonal and placental factors. This decrease lowers the afterload on the heart, allowing cardiac output to rise to meet the increased perfusion needs of the placenta and fetus. The reduction is typically about 20–30% from pre-pregnancy levels, with the lowest values in mid-pregnancy around 14–24 weeks, then gradually returning toward baseline by term. This creates the common pattern of lower blood pressure earlier and mid-pregnancy, followed by normalization as pregnancy progresses. The other options don’t fit because SVR does not increase, remain unchanged, or fluctuate without a clear pattern during normal pregnancy.

Systemic vascular resistance falls during pregnancy due to widespread vasodilation driven by hormonal and placental factors. This decrease lowers the afterload on the heart, allowing cardiac output to rise to meet the increased perfusion needs of the placenta and fetus. The reduction is typically about 20–30% from pre-pregnancy levels, with the lowest values in mid-pregnancy around 14–24 weeks, then gradually returning toward baseline by term. This creates the common pattern of lower blood pressure earlier and mid-pregnancy, followed by normalization as pregnancy progresses. The other options don’t fit because SVR does not increase, remain unchanged, or fluctuate without a clear pattern during normal pregnancy.