Ultrasound and histological measurements of dividing membrane thickness in twin gestations

Objective To determine how prenatal ultrasound measurements of dividing membrane thickness correlate with postnatal histological measurements and chorionicity in twin gestations. Methods This was a prospective, longitudinal cohort study of twin gestations. Dividing membrane thickness was measured by transabdominal ultrasound, with the insonation beam both parallel and perpendicular to the membrane, in the second or third trimester, depending on when care was established. Ultrasound examinations were performed every 4weeks following initial assessment until delivery. Measurements of membrane thickness from the first ultrasound examination were compared with histological measurements after delivery. Results A total of 45 twin pregnancies (32 dichorionic, 13 monochorionic) were included. Mean gestational age at initial ultrasound examination was 24.1 +/- 7.3weeks. Parallel ultrasound measurements of membrane thickness were 1.6 +/- 0.8mm for monochorionic and 2.5 +/- 0.9mm for dichorionic gestations (P = 0.001). Perpendicular ultrasound measurements were 1.6 +/- 0.3mm for monochorionic and 2.2 +/- 0.8mm for dichorionic gestations (P = 0.009). Inter-and intraobserver reliability of ultrasound measurements were 0.847 and 0.950, respectively. Parallel and perpendicular ultrasound measurements correlated better with each other (R = 0.807, P < 0.001) than with histological measurements of membrane thickness (R-parallel = 0.538, P < 0.001; R-perpendicular = 0.529, P < 0.001). Receiver-operating characteristics curve analyses to predict histological membrane thickness > 50th percentile resulted in an area under the curve (AUC) of 0.828 for parallel (P < 0.001) and 0.874 for perpendicular P < 0.001) measurements with a cut-off value of 1.9mm for both approaches. The AUCs for parallel and perpendicularmeasurements to predict dichorionicity were 0.892 (P < 0.001) and 0.823 (P < 0.001) with cut-off values of 1.9 and 1.8 mm, respectively. Conclusion Prenatal ultrasound measurement of twin dividing membrane thickness is positively correlated with postnatal histological measurement. Dichorionicity can be determined by a magnified dividing membrane thickness >= 1.9 mm. Measurements with the ultrasound beam parallel to the dividing membrane may be more accurate than perpendicular measurements. Copyright (C) 2016 ISUOG. Published by John Wiley & Sons Ltd.