Major decrease in the incidence of trisomy21 at birth in south Belgium: mass impact of triple test?

In South Belgium (Wallonia), the 'triple test' was introduced in 1990-1991, and is nowadays a widely accepted screening method for assessment of triso my 21 risk in pregnancy. The 'triple test' is not regulated and can be free ly performed by any biomedical lab, making epidemiological data unavailable . By contrast, cytogenetic investigations are limited to a few genetic cent res, and accurate statistics can be easily built from their files. During t he period 1984-1989, a total of 244 trisomy 21 (1/876 pregnancies) were dia gnosed in the Genetic Centres of Liege and Loverval, 42 (17%) of them prena tally. During the period 1993-1998, 294 trisomy 21 (1/704 pregnancies) were observed, 165 (56%) of which prenatally, and more than 90% of affected pre gnancies were terminated. Even after correction for late foetal loss of tri somic foetuses, the difference is highly significant, and corresponds to a theoretical shift in the incidence of trisomy 21 at birth from 1/794 to 1/1 606. As no remarkable progress occurred in other non-invasive prenatal scre ening procedures or general health care policies in Belgium, the most reaso nable explanation is the use on a large scale of triple test by pregnant wo men, and the election of termination for most affected pregnancies.