Maternal serum markers for Down's syndrome pregnancies.

Down's syndrome is the most common chromosomal abnormality whose incidence increases with advancing maternal age. However, approximately 70% of all Down's syndrome foetuses occur in mothers aged less than 35. Maternal serum markers have been used in an attempt to identify Down's syndrome pregnancies in these low risk mothers. Numerous second trimester maternal serum markers have been documented in the literature and these are reviewed. The Triple test which uses second trimester maternal serum levels of alpha-feto protein, human chorionic gonadotrophin and unconjugated oestriol is the most popular combination in use today. Although it is associated with a 58% detection rate for Down's syndrome pregnancies at a false positive rate of 5%, the Triple test has its problems and these are discussed. The cost-effectiveness of Down's syndrome screening using the Triple test and its role in mothers aged 35 years or more are also explored. Several workers have reported on first trimester serum markers of foetal Down's syndrome but more data is needed before a first trimester serum screening programme for Down's syndrome is possible.