EFFECT OF MATERNAL AGE CURVE ON THE PREDICTED DETECTION RATE IN MATERNAL SERUM SCREENING FOR DOWN-SYNDROME

The effect of the choice of maternal age-specific prevalence curve on the model predicted Down syndrome detection rate was examined. All 19 published regression curves from 11 birth prevalence series in four me ta-analyses were included. The detection rate for a five per cent fals e-positive rate was estimated for three combinations of markers. For f ree beta human chorionic gonadotropin and alpha-fetoprotein the lowest predicted detection rate was 62.3 per cent and the highest 64.1 per c ent, a range of 1.8 per cent. When unconjugated oestriol was added as a third marker it was 65.6-67.3 per cent, a 1.7 per cent range, and wh en inhibin A was the fourth marker the detection rate was 72.0-73.4 pe r cent, a 1.4 per cent range. The number of series included in the reg ression had the biggest effect: when the authors had used a subset tho ught to have the highest ascertainment the predicted detection rate ge nerally increased. The type of regression equation used and restrictio ns on the age range over which the regression was performed were less important factors. The effect of the choice of curve on the predicted increase in detection achieved by incorporating additional markers was relatively small: 3.1-3.3 per cent for unconjugated oestriol and a fu rther 6.1-6.5 per cent for inhibin A. This analysis shows that the mod el inaccuracy caused by the maternal age curve is not small but is unl ikely to be large enough to influence Down syndrome screening policy d ecisions. (C) 1998 John Wiley & Sons, Ltd.