The sensitivity of the trivariate analysis using maternal serum alpha-feto protein, human chorionic gonadotrophin and maternal age in screening for fetal aneuploidy in mothers above the age of 35.

This study was undertaken to assess the usefulness of maternal serum human chorionic gonadotrophin, alpha-fetoprotein and maternal age in screening for fetuses with abnormal chromosomes in pregnant women aged 35 years and over. From 1989 to 1991, 1208 women seen at the National University Hospital had karyotyping procedures performed for maternal age > 35 years as well as second trimester serum samples taken for alpha-fetoprotein and human chorionic gonadotrophin. Sixteen (1.3%) chromosomal abnormalities were present. Using cut off risk levels of 1:250 and 1:384, the sensitivity of the analysis in screening for Down's syndrome pregnancies was 71.5% and 86% respectively. For the non Down's chromosomal abnormalities, using cut off risk levels of 1:250 and 1:384, the sensitivity of the analysis was only 22.3% and 33.4% respectively. Thus risk calculations based on the two serum markers and maternal age failed to identify all fetuses with abnormal chromosomes.