Screening for Down's syndrome in the North East Thames region.

The suggested strategies for a screening programme for Down's syndrome by maternal serum alpha fetoprotein concentration were examined and tested on the experience of the North East Thames Regional. Screening by maternal serum alpha fetoprotein concentration may be used to identify pregnancies at increased risk, but this is useful only in women aged over 32 whose collective risk is greater than one in 200. The absolute probability of carrying babies with Down's syndrome for individuals in this high risk group can then be calculated and used to decide whether further diagnosis by amniocentesis is desired.