Cytogenetic aspects of the Canadian early and mid-trimester amniotic fluidtrial (CEMAT)

Cytogenetic results from a large multicentre randomized controlled study of 2108 amniotic fluids obtained at 11+0-12+6 weeks (EA) and 1999 fluids at 1 5+0-16+6 weeks (MA) were compared. There was no statistically significant d ifference in the rate of chromosome abnormalities (EA =1.9 per cent; MA=1.7 per cent) or level III mosaicism (EA=0.2 per cent; MA=0.2 per cent) betwee n the groups. Level I and Level II mosaicism occurred more frequently in MA . Maternal cell contamination was not significantly different between the gro ups, but maternal cells only were analysed from one bloody EA fluid. The number of repeat amniocenteses because of cytogenetic problems was 2.2 per cent in the EA group compared with only 0.3 per cent in the MA group. O n average, culture of EA fluids required one day more than MA fluids. Although both culture success (97.7 per cent) and accuracy (99.8 per cent) were high for patients randomized to the EA group, routine amniocentesis pr ior to 13 weeks' gestation is not recommended for clinical reasons includin g an increased risk of fetal loss and talipes equinovarus. Copyright (C) 19 99 John Wiley & Sons, Ltd.