Ultrasound Measurement of the Fetal Adrenal Gland as a Predictor of Spontaneous Preterm Birth
OBJECTIVE: To estimate whether ultrasound measurement of the fetal adrenal gland remote from delivery in asymptomatic women can accurately predict spontaneous preterm birth. METHODS: We conducted a prospective multicenter observational nested cohort study of asymptomatic nulliparous women with a singleton pregnancy to study adverse pregnancy outcomes. Between 22 0/7 and 30 6/7 weeks of gestation, credentialed ultrasonographers measured the width (width), length (length), and, when able, depth (depth) of the "fetal zone" of the fetal adrenal gland as well as the width (Width), length (Length), and depth (Depth) of the total gland. We used the ratios of each measurement (width/Width, length/Length, and depth/Depth) to control for variation in adrenal size by gestational age. The accuracy of each ratio measurement in predicting spontaneous preterm birth at less than 37 0/7 weeks of gestation and spontaneous preterm birth at less than 34 0/7 weeks of gestation was assessed by receiver operating characteristic curves using area under the curve. RESULTS: Pregnancy outcomes were available for 1,697 women with one or more fetal adrenal gland measurements. Spontaneous preterm birth at less than 37 0/7 weeks of gestation and spontaneous preterm birth at less than 34 0/7 weeks of gestation occurred in 82 (4.8%) and six women (0.4%), respectively. None of the fetal adrenal gland measurements distinguished spontaneous preterm birth from term birth. The areas under the curve (95% confidence intervals) for spontaneous preterm birth at less than 37 0/7 weeks of gestation were 0.51 (0.45-0.58), 0.50 (0.44-0.56), and 0.52 (0.41-0.63) for width/Width, length/Length, and depth/Depth ratios, respectively. The areas under the curve for spontaneous preterm birth at less than 34 0/7 weeks of gestation were 0.52 (0.25-0.79) and 0.55 (0.31-0.79) for width/Width and length/Length ratios, respectively. Additionally, none of the means of the gland measurements were statistically different between those delivering at term and spontaneous at preterm (P>.05). CONCLUSION: Fetal adrenal size, as measured by ultrasonography between 22 0/7 and 30 6/7 weeks of gestation, is not predictive of spontaneous preterm birth in asymptomatic nulliparous women.