Role of early second-trimester uterine artery Doppler screening to predict small-for-gestational-age babies in nulliparous women

Abstract

Background: Trophoblastic invasion of the uterine spiral arteries substantially increases compliance to accommodate increased blood flow to the placenta. Failure of this process impedes uterine artery blood flow, and this may be detected by uterine artery Doppler flow studies. However, the clinical utility of uterine artery Doppler flow studies in the prediction of adverse pregnancy outcomes in a general population remains largely unknown.

Objective: We sought to determine the utility of early second-trimester uterine artery Doppler studies as a predictor of small-for-gestational-age neonates.

Study design: Nulliparous women with a viable singleton pregnancy were recruited during their first trimester into an observational prospective cohort study at 8 institutions across the United States. Participants were seen at 3 study visits during pregnancy and again at delivery. Three indices of uterine artery Doppler flow (resistance index, pulsatility index, and diastolic notching) were measured in the right and left uterine arteries between 16 weeks 0 days' and 22 weeks 6 days' gestation. Test characteristics for varying thresholds in the prediction of small for gestational age (defined as birthweight <5th percentile for gestational age [Alexander growth curve]) were evaluated.

Results: Uterine artery Doppler indices, birthweight, and gestational age at birth were available for 8024 women. Birthweight <5th percentile for gestational age occurred in 358 (4.5%) births. Typical thresholds for the uterine artery Doppler indices were all associated with birthweight <5th percentile for gestational age (P < .0001 for each), but the positive predictive values for these cutoffs were all <15% and areas under receiver operating characteristic curves ranged from 0.50-0.60. Across the continuous scales for these measures, the areas under receiver operating characteristic curves ranged from 0.56-0.62. Incorporating maternal age, early pregnancy body mass index, race/ethnicity, smoking status prior to pregnancy, chronic hypertension, and pregestational diabetes in the prediction model resulted in only modest improvements in the areas under receiver operating characteristic curves ranging from 0.63-0.66.

Conclusion: In this large prospective cohort, early second-trimester uterine artery Doppler studies were not a clinically useful test for predicting small-for-gestational-age babies.

Keywords: Doppler ultrasound; gestational hypertension; small for gestational age; spontaneous preterm birth; uterine artery.

Figure 1

Participant flow chart demonstrates that 10,038 women were enrolled into the nuMoM2b study, 9,473 are known to have delivered after 20 weeks, and 8,050 of these women underwent successful uterine artery Doppler studies between 16 weeks 0 days and 22 weeks 6 days (excluding fetal demise, bradycardia, tachycardia, major structural malformation, and hydrops). For the 8,050 women with uterine artery Doppler measurements: 8,024 could be used in analysis on small for gestational age; 8,033 on hypertensive disorders of pregnancy; 8,046 on spontaneous preterm birth; and all 8,050 on stillbirth.

Figure 2

Receiver operator characteristic curves were generated to demonstrate the ability of uterine artery Doppler measurements to predict small for gestational age (birth weight <5^th percentile for gestational age at delivery). A. Contrasts diastolic notch depth, resistance index (RI), and pulsatility index (PI) on continuous scales; B. Contrasts diastolic notch depth thresholds; C. Contrasts RI thresholds; and D. Contrasts PI thresholds. “Suggested” thresholds are from the literature. “Optimized” thresholds are those maximizing the sum of sensitivity and specificity.

Figure 3

Receiver operator characteristic curves were generated to demonstrate the ability of uterine artery Doppler measurements and maternal demographic variables to predict small for gestational age (birth weight <5^th percentile for gestational age at delivery). Demographic variables that were included in the predictive model included early pregnancy body mass index, race/ethnicity, smoking, maternal age, chronic hypertension, and pre-gestational diabetes. A. Contrasts diastolic notch depth, resistance index (RI), and pulsatility index (PI) on continuous scales; B. Contrasts diastolic notch depth thresholds; C. Contrasts RI thresholds; and D. Contrasts PI thresholds. “Suggested” thresholds are from the literature. “Optimized” thresholds are those maximizing the sum of sensitivity and specificity.