Reference Values for Sonographically Estimated Fetal Weight in Twin Gestations Stratified by Chorionicity: A Single Center Study.

Objectives: To determine reference values for sonography-based estimated fetal weight (EFW) in twin gestations in one single tertiary medical center in the United States.

Methods: A retrospective longitudinal analysis of EFW evaluations of fetuses of twin gestations between November 2006 and June 2016. Fetuses with major congenital anomalies or chromosomal abnormalities were excluded. Estimated fetal weight was calculated using the Hadlock 1985 formula. Linear mixed models were used to allow for multiple but inconsistent observations among individuals, and to account for intertwin differences as well as for gender. Reference values were constructed using a best-fit regression model for estimation of mean and standard deviation at each gestational age after normalization of variables. Chorionicity-specific curves were constructed.

Results: A total of 5515 ultrasound examinations were performed in 2115 twin pregnancies between 24 and 38 weeks of gestation (2.6 ± 4.0 scans/pregnancy). Values corresponding to the 5th, 10th, 50th, 90th, and 95th percentiles for EFW are presented for every gestational age. At 28, 32, and 36 weeks, values were as follows: 855, 1109, and 1363 g; 1351, 1732, and 2294 g; and 1363, 2112, and 2881 g for the 10th, 50th, and 90th percentiles, respectively. Chorionicity-specific curves are presented for comparison with previously published references.

Conclusions: Reference values for sonographic-based fetal growth are presented for clinical and research use.