First trimester screening for trisomy 21 in gestational week 8-10 by ADAM12-S as a maternal serum marker

Table 3 Empirical results

	1 in 100		1 in 250
	FPR (95% CI)	DR (95% CI)	FPR (95% CI)	DR (95% CI)
(i) maternal age, PAPP-A & free B-hCG	2.9 (1.5, 4.2)	72.2 (65.7, 78.7)	9.4 (7.0, 11.8)	86.2 (79.0, 93.3)
(ii) maternal age, PAPP-A, free B-hCG & ADAM12-S	2.6 (1.3, 3.9)	73.7 (67.7, 79.6)	9.3 (7.0, 11.7)	87.3 (80.4, 94.2)
(iii) maternal age, PAPP-A, free B-hCG & NT	0.6 (0.1, 1.2)	71.1 (61.8, 80.5)	2.8 (1.5, 4.1)	83.7 (75.7, 91.8)
(iv) maternal age, PAPP-A, free B-hCG, NT & ADAM12-S	0.7 (0.1, 1.3)	71.1 (61.8, 80.5)	2.6 (1.4, 3.8)	87.7 (80.4, 94.9)
(v) maternal age, PAPP-A & ADAM12-S	2.5 (1.4, 3.7)	56.8 (50.1, 63.5)	9.2 (6.9, 11.4)	73.7 (63.6, 83.8)
(vi) maternal age, PAPPA, ADAM12-S & NT	1.4 (0.6, 2.3)	75.1 (67.2, 83.1)	3.5 (2.2, 4.9)	81.4 (75.3, 87.6)

Results for a screening test including maternal age, PAPP-A and ADAM12-S, with and without NT. These results are empirical values, standardised to a reference maternal age population (UK 2000 to 2002). Detection rates and false-positive rates for fetal trisomy 21 at fixed risk cut-offs of 1 in 100 and 1 in 250 are given. Figures in brackets are 95% confidence intervals. Substantial decrease in DR when first trimester free B-hCG in (i) is replaced with ADAM12-S to give (v), with a negligible decrease in FPR.
Substituting free B-hCG in the combined test (iii) for ADAM12-S to give (vi), gives a slightly higher DR and FPR at a risk cut-off of 1 in 100, and a slightly lower DR and higher FPR at a risk cut-off of 1 in 250.

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