Amniotic fluid alpha-fetoprotein, gamma-glutamyltranspeptidase, and autosomal trisomies.

Alpha-fetoprotein (AFP) concentration and gamma-glutamyltranspeptidase (GGT) activity have been analysed in amniotic fluid from a series of 65 pregnancies with autosomal trisomies. AFP values were reduced on average to 60 per cent of normal in cases of trisomy 21, but were not significantly different from normal in cases of trisomies 18 and 13. GGT activities were uniformly lower (44 per cent of normal) for all types of autosomal trisomy. A review of the literature indicates that over 85 per cent of Down's pregnancies but only 39 per cent of trisomy 18 and 13 pregnancies have amniotic fluid AFP levels below the normal median value, while the corresponding figures for GGT are 91 per cent for Down's syndrome and 96 per cent for trisomies 18 and 13.