Taylor MJO, Fisk NM.
Multiple pregnancy
The Obstetrician and Gynaecologist 2000; 2(4); 4-10.

A review of twin complications, antepartum and intrapartum management including the importance of chorionicity determination.

Carroll SGM, Soothill PW, Abdel-Fattah SA, Porter H, Montague I, Kyle PM.
Prediction of chorionicity in twin pregnancies at 10-14 weeks of gestation.
BJOG 2002; 109: 182-187, Abstract.

Chorionicity should be defined between 11-14 weeks, when the most recent evidence suggests that it can be correctly identified 99% of the time.

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