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Evaluation of the twin peak or lambda sign in determining chorionicity in multiple pregnancy
S L Wood1, R St Onge, G Connors
1Department of Obstetrics and Gynecology, University of Calgary, Canada.
Objective:
To assess prospectively the diagnostic capabilities of ultrasound assessment, using the twin peak or lambda sign, in determining chorionicity in multiple pregnancy.
Methods:
Fifty-five cases of multiple pregnancy were assessed. Real-time ultrasound scans of the origin of the inter-twin membrane for the presence or absence of the twin peak/lambda sign were performed and permanent images recorded. Chorionicity was determined by placental pathologic analysis.
Results:
Presence or absence of the twin peak/lambda sign as determined by real-time ultrasound correctly predicted chorionicity in 34 of 36 dichorionic and seven of eight monochorionic twin pregnancies: sensitivity for dichorionicity 94%, specificity 88%, positive predictive value 97%, and negative predictive value 78%. Real-time assessment was superior to analysis of permanent films.
Conclusion:
Ultrasound assessment of chorionicity using the twin peak/lambda sign has high sensitivity and specificity, but accuracy may not be sufficient to guide clinical management in all cases.