Chorionicity determination in twin pregnancies: how accurate are we?
OBJECTIVE
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.
Stenhouse
E
E
Department of Obstetrics and Gynaecology, Glasgow Royal Maternity Hospital, Glasgow, UK.
Hardwick
C
C
Maharaj
S
S
Webb
J
J
Kelly
T
T
Mackenzie
F M
FM
D000293:Adolescent; D000328:Adult; D002823:Chorion / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D005260:Female; D005865:Gestational Age; D006801:Humans; D010920:Placenta / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D011247:Pregnancy; D011256:Pregnancy Outcome; D011272:Pregnancy, Multiple; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D014427:Twins; D016216:Ultrasonography, Prenatal / Q000379:methods*; D006113:United Kingdom