Epidemiology of chromosomal trisomies in the East of Ireland.

Background: Chromosomal trisomies are associated with advancing maternal age. In Ireland, information on the total prevalence and outcome of trisomy affected pregnancies is unavailable. This study aimed to ascertain more precise data on Trisomies 21, 18 and 13 in a large Irish region during the period 2011-2013.

Methods: Multiple information sources were used in case finding, including a regional congenital anomaly register, all maternity and paediatric hospitals in the region and the regional Department of Clinical Genetics.

Results: There were 394 trisomy cases from 80 894 total births, of which 289 were Trisomy 21, 75 were Trisomy 18 and 30 were Trisomy 13. The total prevalence rate was 48.9/10 000 births, 35.7, 9.3 and 3.7 for Trisomies 21, 18 and 13, respectively. Over 90% of Trisomies 18/13 and 47% of Trisomy 21 were diagnosed prenatally; 61% of Trisomy 21 cases and nearly 30% of Trisomies 18/13 were live births; 38% all trisomy affected pregnancies ended in a termination.

Conclusions: This study provides precise data on the total prevalence and outcome of trisomy affected pregnancies in the East of Ireland. Total prevalence rates were higher than previously reported. Prenatal diagnosis had a significant impact on outcome. These data provide a better basis for planning of services for live-born children affected by trisomy.