Evaluation of the twin peak or lambda sign in determining chorionicity in multiple pregnancy.
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.


CONCLUSIONS
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.
Wood
S L
SL
Department of Obstetrics and Gynecology, University of Calgary, Canada.
St Onge
R
R
Connors
G
G
Elliot
P D
PD
D002823:Chorion / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D011237:Predictive Value of Tests; D011247:Pregnancy; D011272:Pregnancy, Multiple; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal