Socioeconomic inequalities in placental vascular resistance: a prospective cohort study.

OBJECTIVE:To examine the association between socioeconomic position (SEP) and umbilical and uterine placental resistance indices in the second and third trimester, and to what extent this could be explained by lifestyle-related behaviors. DESIGN:Prospective cohort study. SETTING:Rotterdam, the Netherlands. PATIENT(S):7,033 pregnant women of mean age (± standard deviation) 29.9 (±5.2) years. INTERVENTION(S):None. MAIN OUTCOME MEASURE(S):Uterine artery resistance index (UARI) and umbilical artery pulsatility index (UAPI) in second and third trimester measured with Doppler ultrasound. RESULT(S):Third-trimester UARI and both second- and third-trimester UAPI were statistically significantly higher for women with lower educational levels as compared with those with higher educational levels. Educational level was strongly associated with the risk of continuously high levels of UARI and UAPI from second to third trimester of pregnancy. Notching was not associated with SEP. Smoking was a significant contributor to the association of SEP and increased placental resistance indices; body mass index, folic acid supplementation use, and alcohol use were not. CONCLUSION(S):Women from low socioeconomic subgroups have higher placental resistance indices, which may cause a higher prevalence of pregnancy complications. This was mainly explained by maternal smoking during pregnancy.