Trisomy 21 – incidence, diagnostics and pregnancy terminations 1999–2018

BACKGROUND: We hypothesised that the examinations offered to pregnant women at fetal medicine centres differ from those offered to other pregnant women in Norway. We therefore wanted to investigate the incidence, prenatal diagnostics and pregnancy terminations in cases of trisomy 21. We also wanted to compare the figures from the National Center for Fetal Medicine, St Olav's Hospital, Trondheim University Hospital, with national figures for Norway. MATERIAL AND METHOD: We analysed figures for the period 1999-2018 retrospectively. National data were compared with an unselected population whose local hospital is St Olav's Hospital. National figures were retrieved from the Medical Birth Registry of Norway and local figures were from the quality registry at the National Center for Fetal Medicine. RESULTS: The national incidence of trisomy 21 was 0.20 %, varying from 0.14 % to 0.23 %, and showed a significant increase over time (p < 0.01). The increasing incidence showed an association with increasing age in the women (p < 0.01). The incidence of live births was stable, even though the proportion of pregnancy terminations increased. In the local population, the incidence of trisomy 21 was 0.19 %. A total of 68.2 % of the local population were diagnosed prenatally, and 87.7 % of these pregnant women terminated the pregnancy. There was a significantly higher proportion of pregnancy terminations in the local population than in the remainder of the national population (p < 0.01). INTERPRETATION: The difference in the proportion of pregnancy terminations may be associated with variation in access to prenatal diagnostics.