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Abstract

We appreciate your interest in our recent Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-be (nuMoM2b) Network article, entitled, “Uterine artery Doppler studies in the early second trimester to predict abnormal pregnancy outcome in nulliparous women.”1Parry S. Sciscione A. Haas D.M. et al.Role of early second-trimester uterine artery Doppler screening to predict small-for-gestational-age babies in nulliparous women.Am J Obstet Gynecol. 2017; 217: 594.e1-594.e10Abstract Full Text Full Text PDF Scopus (34) Google Scholar Because of the inaccuracy of prenatal ultrasound scans for the estimation of fetal weight late in pregnancy, we intentionally selected birthweight rather than ultrasound-based estimated fetal weight as our primary outcome. However, we acknowledge that SGA birthweights do not consider newborn infant height and that the ponderal index (birthweight/height3×100) may reflect more accurately asymmetric fetal growth restriction that is caused by abnormal uteroplacental circulation. Unfortunately, length boards were not used routinely at nuMoM2b Network sites to measure newborn heights accurately, and other measurements of newborn infant height are inaccurate. We agree that the angle of insonation at measurement affects the uterine artery flow waveforms. Consequently, we used ratios (resistance index, pulsatility index) to account for the angle of insonation. We did not measure depth of the diastolic notch as a ratio as suggested (peak diastolic flow/flow at the depth of the notch), because that is not the technique used at the nuMoM2b Network sites. Hence, our conclusion may be modified to report that early second-trimester uterine artery Doppler studies, as commonly used in the United States, were not a clinically useful test for the prediction of small-for-gestational-age babies, and the ratio for the measurement of the end diastolic notch and computer analyses of uterine artery flow velocity waveforms may be the foci of future research. There are a number of ways to study the ability of uterine artery Doppler studies to predict adverse pregnancy outcomes, and we are confident that the analytical methods we used for studying small-for-gestational-age babies as a primary outcome and preeclampsia or gestational hypertension preceding labor, spontaneous preterm birth, and stillbirth as secondary outcomes were appropriate. We did not include placental abruption among our outcomes, because placental abruption is a clinical diagnosis that is difficult to validate in such a large, multicenter study. We acknowledge that the analysis of adverse pregnancy outcomes that are associated with abnormal uteroplacental circulation as a composite primary outcome (ie, fetal growth restriction, gestational hypertension, spontaneous preterm birth, and placental abruption) will affect predictive values of the test, but we dispute the clinical utility of the composite outcome. More specifically, how could the prediction of a composite of adverse pregnancy outcomes affect clinical care, because the prevention of the different adverse pregnancy outcomes varies? Consequently, we are confident that our analytical methods optimally assessed the clinical utility of uterine artery studies as performed in multiple centers across the United States. Uterine artery Doppler studies in the early second trimester to predict abnormal pregnancy outcome in nulliparous womenAmerican Journal of Obstetrics & GynecologyVol. 219Issue 4PreviewWe read with interest the recent article from the Nulliparous Pregnancy Outcomes Study: Monitoring Mothers-to-be.1 This multi-centered US study includes a large data set (8000 pregnancies) that potentially provides good data on most known adverse pregnancy outcomes related to abnormal uteroplacental circulation.2 Full-Text PDF