Trisomy 18 fetuses with cystic hygroma linked to positive maternal serum Down's syndrome Triple test screening result.

The maternal serum triple screen of a-fetoprotein, unconjugated oestriol and human chorionic gonadotrophin (hCG) concentrations is a well-validated screening test for Down’s syndrome. 1 The triple test markers can also be used to identify pregnancies at increased risk of trisomy 18.2 Cystic hygroma is associated with an increased risk of Down’s syndrome,3 as it is with trisomy 18.4–6Here we describe two cases of trisomy 18 with a typical Down’s syndrome pattern because of the presence of hygroma that may have resulted in a high hCG level rather than a low one.