Table 1

Assumptions made from published data in predicting the effects of screening strategies

	Age related amniocentesis	Maternal serum screening	Fetal echocardiography
Assumed uptake of test	50^1-150	81	91
Assumed detection rate	100	61/91^1-151	15
Assumed amniocentesis rate		83/59^1-151	75
Assumed termination rate	100	90	100
Effective reduction	50	37/39^1-151	10
Proportion of population screened^1-152	33	100	34
Total effective reduction^1-164	17	37/39^1-151	3

↵1-150 Mothers 35 and over.
↵1-151 Under 35/35 and over.
↵1-152 ie % of mothers 35 and over or % of fetuses with CHD.
↵1-164 Allowing for prevalence of maternal age ≥ 35 or prevalence of congenital heart disease in the fetus.