First-trimester ultrasound determination of chorionicity in twin pregnancy

Authors


Abstract

Objective

To determine the accuracy of ultrasound at 11–14 weeks' gestation in the diagnosis of chorionicity in twin pregnancy.

Methods

This was a retrospective observational study of data obtained between 1999 and 2010. At the first-trimester routine ultrasound scan, chorionicity was assigned according to the number of placental masses and T or λ-signs for a single placental mass. Chorionicity was confirmed by histology or discordant sex at birth.

Results

A total of 648 pregnancies were assigned chorionicity by first-trimester ultrasound during the study period. Chorionicity was ascertained in 613 cases, either by histology (n = 340) or discordant sex (n = 273). Chorionicity was correctly assigned by ultrasound at 11–14 weeks in 612 of 613 pregnancies (accuracy 99.8%). Sensitivity and specificity for determining monochorionicity were 100% and 99.8%, respectively.

Conclusions

First-trimester ultrasound can be used to determine chorionicity reliably by noting the number of placental masses and T or λ-signs. Determination of twin chorionicity is important and should be completed in the first trimester. Copyright © 2011 ISUOG. Published by John Wiley & Sons, Ltd.

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