Chorionicity determination in twin pregnancies: how accurate are we?

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Abstract
Objectives: To determine the accuracy of antenatal prediction of chorionicity in twin pregnancies in our institution.Methods: Antenatal chorionicity was determined using the number of placental masses, the presence or absence of a twin peak sign and the fetal sex. The gestational age at assessment was documented. Postnatal diagnosis of chorionicity was determined by neonatal sex and placental pathology.Results: Chorionicity was correctly determined in 95% of cases (n = 131); 91% of the monochorionic and 96% of the dichorionic pregnancies were correctly determined. If chorionicity was assessed prior to 14 weeks' gestation (n = 96) the correct diagnosis was made in all except one case.Conclusions: Ultrasound assessment of chorionicity has a high sensitivity and specificity. This is further improved if the assessment is performed prior to 14 weeks' gestation. Copyright © 2002 ISUOG