Ultrasound has been found to be extremely accurate in diagnosing the c
horionicity of multiple gestations. Prenatal counselling and/or planni
ng for selective termination is most often based on the sonographic pr
ediction of chorionicity. We present a case of triplet pregnancy in wh
ich early sonographic prediction of chorionicity did not match the pat
hological diagnosis at delivery. (C) 1998 John Wiley & Sons, Ltd.