Table 1.

Likelihood ratio and maternal age‐adjusted probability of the IONA® test, tabulated against results of the reference method (amniocentesis, chorionic villus sampling or birth outcome), for detection of trisomies 21, 18 and 13 in 437 maternal serum samples, using a probability risk cut‐off of ≥ 1 in 150

	Reference method
IONA test result	Unaffected	Trisomy	Total
Likelihood ratio
Unaffected	378	0	378
Trisomy 21	1	43	44
Trisomy 18	0	10	10
Trisomy 13	0	5	5
Total	379	58	437
Age‐adjusted probability
Unaffected	379	0	379
Trisomy 21	0	43	43
Trisomy 18	0	10	10
Trisomy 13	0	5	5
Total	379	58	437