Local norms of maternal serum alpha-fetoprotein values in early second trimester: a prelude to a Down's syndrome screening programme incorporating maternal serum alpha-fetoprotein values.

Maternal alpha-fetoprotein in (MSAFP) has recently been proposed for screening of Down's syndrome. This is based on the association of a lowered MSAFP level at a given gestational age in Down's syndrome (DS) pregnancies. Most conventional 'screening' programmes in DS are based on the maternal age alone, selecting older mothers, who are at greater risk of having a DS infant born, for antenatal karyotyping. However, as 75% of DS infants are born to mothers less than 35 years old, a combination of blood tests including MSAFP and maternal age as independent risk factors would screen the younger mothers as a good cost-benefit ratio in selecting the 'at-risk' mothers for karyotyping. In this study, the gestational age was calculated from the first day of the last menstrual period (LMP) as well as from ultrasound cephalometry. The local MSAFP levels follow the same trend at a slightly higher level as those based on clinical evaluation of the Abbot AFP-EIA Monoclonal kits.