Second- and third-trimester placental hemodynamics and the risks of pregnancy complications: the Generation R Study.

Characteristics of the uterine and umbilical artery blood flow patterns are indirect measures of uteroplacental circulation. We examined whether uterine and umbilical artery resistance indices are influenced by maternal demographic and lifestyle characteristics, track from the second trimester to the third, and are associated with the risk of pregnancy complications. This analysis was embedded among 7,660 pregnant women in the Generation R Study (Rotterdam, the Netherlands, 2001-2005). Placental resistance indices were assessed in the second and third trimesters. Information about pregnancy outcomes was obtained from medical records. Maternal characteristics affected second- and third-trimester placental resistance indices. Correlation coefficients for correlation between the second and third trimesters were 0.50 and 0.32 for uterine artery resistance index and umbilical artery pulsatility index, respectively. Higher placental resistance indices in the second and third trimesters and persistence in the highest tertile of uterine artery resistance index from the second trimester to the third were associated with the risks of preeclampsia, preterm birth, and small size for gestational age at birth (all P's < 0.05). Our study shows that placental resistance indices are influenced by maternal demographic and lifestyle characteristics and track moderately from the second trimester to the third. Increased placental resistance indices in the second and third trimesters are associated with increased risks of adverse pregnancy outcomes.