Longitudinal reference range for umbilical cord cross-sectional area in twin pregnancies at 18-32 weeks of gestation.

Objectives: The objectives of this study were to establish gestational age-specific reference ranges for cross-sectional area of the umbilical cord, and its components, in twin pregnancies and to compare them with previously reported singleton reference ranges.
Methods: This was a prospective longitudinal study involving uncomplicated dichorionic twin pregnancies. Sonographic measurements of the cross-sectional area of the umbilical cord, umbilical vein and arteries and Wharton's jelly were obtained in a plane adjacent to the fetal abdomen, every 3 weeks, between 18 and 32 weeks of gestations. Multilevel regression analysis was used to determine gestational age-specific reference ranges for each parameter, and these were plotted against singleton pregnancy references.
Results: Three hundred and thirty four ultrasound scans were performed in 44 twin pregnancies, between 18 and 32.9 weeks (mean: 3.8 ± 0.7 scans/pregnancy and mean interval between scans: 3.3 ± 0.9 weeks). All umbilical cord cross-sectional areas (total, vein, artery and Wharton's jelly) showed a significant increase with gestational age. Compared with singleton pregnancy ranges, mean values were considerably lower in twin pregnancies and resemble the lower limits observed in singletons.
Conclusion: In twin pregnancies, cross-sectional area of the umbilical cord, and its components, increases between 18 and 32 weeks, and mean values are substantially lower compared with singleton pregnancies.
(© 2015 John Wiley & Sons, Ltd.)