OBJECTIVE: To evaluate time of diagnosis of 22q11.2 deletion and 22q11.2 duplication as well as trisomies 21, 13, and 18 before and after introduction of a prenatal screening program including combined first-trimester screening for the trisomies in Denmark in 2004.

METHOD: Cross-sectional, population-based register study employing The Danish Cytogenetic Central Register. Proportions of cases diagnosed 1998-2004 and 2005-2017 were compared before 14+0 and 22+0 weeks and birth (prenatal cases) or up to 1 or 10 years of age (postnatal cases).

RESULTS: In total, 4,562 cases were included. From 1998-2004 to 2005-2017, the proportion of 22q11.2 deletion cases identified prenatally increased from 4.3% (95% CI: 0.9-12.0%) to 27.3% (21.2-34.0%), while for 22q11.2 duplication an increase from 0/6 to 26/87 (prenatal cases/all cases) was observed. Similarly, proportions of trisomies 21, 13, and 18 detected before birth increased. A greater proportion of the studied conditions was identified earlier in pregnancy, but not generally earlier in the postnatal course.

CONCLUSION: Proportions of 22q11.2 deletion and 22q11.2 duplication identified prenatally increased after introduction of a prenatal screening programnot aimed specifically to identify these conditions, . A greater proportion of all cases were detected earlier in pregnancy, but not earlier postnatally, following introduction of screening. This article is protected by copyright. All rights reserved.