[Reference Values for Sonographic Estimated Fetal Weight and Biometry in Twin Gestations - A Nationwide Cohort]

Twin gestations are subjected to higher rates of growth abnormalities. Accurate, locally customized reference values may contribute to an accurate diagnosis of abnormal growth. We aimed to determine reference values for sonographically estimated fetal weight (sEFW) and biometry in twin gestations.

A multicenter retrospective longitudinal analysis of sEFW and biometric measurements evaluations of twin gestations was performed between 2010 and 2022 in 11 medical centers in Israel. The sEFW at 14-40 gestational weeks was calculated using the Hadlock 1985 formula. Only data from viable twins delivered at or above 34 gestational weeks were included. Cases that underwent early fetal reduction or cases that were diagnosed with major congenital fetal anomalies or genetic aberrations were excluded. The non-parametric Quantile Generalized Additive Model (QGAM) approach was employed for building the growth curves.

A total of 7,060 fetuses and 18,248 measurements were incorporated in the sEFW and biometry growth curves. The cohort included 3,449 (49%) dichorionic twins contributing 7,192 (40%) of measurements. The rest were monochorionic twins (536, 8% of twins; 1,866, 10% of measurements) or with unknown chorionicity (3,066, 43% of twins; 9,171, 50% of measurements). The cohort included 49% females and 51% males when gender was reported (N=10,945 evaluations). Similar growth curves were observed when curves were split according to chorionicity, when the cohort included only twins delivered after 36 gestational weeks, and following the exclusion of discordant twins above 30%.

Reference values for twins' sEFW and biometric measurements are presented for the Israeli population for clinical and research use. Since sEFW and biometry reference values determine fetal growth assessment and subsequent pregnancy management, this study has significant implications for Israeli health policy related to twin pregnancy care.