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Am J Obstet Gynecol. 2006 Sep;195(3):863-7.

Antenatal sonographic prediction of twin chorionicity.

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  • 1Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, Columbia University Medical Center, New York, NY 10032, USA.



We sought to determine the accuracy of antenatal diagnosis of twin chorionicity at a single tertiary care center and assess the consequences of incorrect diagnoses.


Twins with chorionicity diagnosed by ultrasound < or = 24 weeks' gestation were retrospectively reviewed. Chorionicity was assigned by sonographic findings including placental location(s), the lambda and T-signs, and/or fetal gender(s). Postnatal diagnosis was determined by placental histopathologic examination. Medical records of antenatal-postnatal discordant chorionicities were reviewed for adverse sequelae.


Chorionicity was correctly assigned antenatally in 392/410 (95.6%) twins. The sensitivity, specificity, and positive and negative predictive values of monochorionicity assessed < or = 14 weeks were 89.8%, 99.5%, 97.8%, and 97.5%. Corresponding statistical values for the second trimester were 88.0%, 94.7%, 88.0%, and 94.7%. Two cases of inaccurate antenatal diagnoses affected patient counseling or were associated with adverse clinical outcomes.


Antenatal assessment of chorionicity is accurate; however, incorrect diagnoses do occur and can affect reliable patient counseling and management.

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