Uterine artery Doppler, birth weight and timing of onset of pre‐eclampsia: providing insights into the dual etiology of late‐onset pre‐eclampsia

Objective To investigate the relationship between uterine artery Doppler ultrasound indices and birth weight in women with early-, intermediate- and late-onset pre-eclampsia as compared with women with uneventful pregnancy outcome. Methods In a retrospective, observational cohort study, uterine artery Doppler assessment was carried out at 18 + 0 to 23 + 6 weeks' gestation in 26 893 women attending for routine antenatal care in a tertiary care center. The mean resistance index (RI) and its relationship to the outcome of pregnancy and birth-weight centiles were evaluated. Results Uterine artery RI showed a significant, negative correlation with birth weight (r = −0.20, P < 0.0001). Patients with early-onset pre-eclampsia had an increased prevalence of high uterine artery mean RI, above the 90th centile, corresponding to an increased proportion of small-for-gestational age (SGA) neonates with a birth weight below the 10th centile. In late-onset pre-eclampsia, however, there was an unexpectedly higher proportion of large-for-gestational-age (LGA) neonates with a birth weight above the 90th centile without a concurrent increase in the prevalence of low uterine artery mean RI below the 10th centile. Conclusions The finding of a bimodal skewed distribution of birth weight, with neonates exhibiting a higher prevalence of both LGA and SGA with late-onset pre-eclampsia, indicates that there are two types of late-onset pre-eclampsia. These findings explain the poor performance of mid-trimester uterine artery Doppler in predicting pre-eclampsia at term and provide insights into the placental origins of the early and late forms of pre-eclampsia. Copyright © 2014 ISUOG. Published by John Wiley & Sons Ltd