Table 2 Estimated livebirth prevalence of T21 in the Netherlands, 2000–2013

Year	Total livebirths	Expected number of T21 livebirths	Natural livebirth prevalence of T21 per 10 000	AC_ToP	CVS_ToP	Actual number of T21 livebirths	Impact of prenatal screening (%)	Livebirth prevalence of T21 per 10 000
2000	206 619	401	19.4	99	63	284	29.2	13.7
2001	202 603	405	20.0	83	75	292	28.0	14.4
2002	202 083	410	20.3	107	77	277	32.3	13.7
2003	200 297	416	20.8	117	100	260	37.4	13.0
2004	194 007	413	21.3	118	108	251	39.2	12.9
2005	187 910	407	21.7	80	104	276	32.1	14.7
2006	185 057	407	22.0	99	107	260	36.1	14.0
2007	181 336	405	22.3	92	125	251	38.0	13.8
2008	184 634	414	22.4	111	141	235	43.3	12.7
2009	185 158	418	22.6	118	123	246	41.2	13.3
2010	184 325	418	22.7	125	141	228	45.4	12.4
2011	180 020	407	22.6	99	114	255	37.3	14.2
2012	175 972	395	22.4	78	127	250	36.7	14.2
2013	171 426	384	22.4	93	128	227	40.8	13.3

Actual number of T21 livebirths = expected number of T21 livebirths − ((AC_ToP × 0.75) + (CVS_ToP × 0.68))
Impact of screening (%) = (expected number of T21 livebirths − actual number of T21 livebirths) / expected number of T21 livebirths
The correction factor for natural foetal loss for women screened by AC was 25% and CVS was 32%
T21 trisomy 21, AC_ToP termination of pregnancy subsequent positive amniocentesis, CVS_ToP termination of pregnancy subsequent positive chorionic villus sampling

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