Descriptive epidemiology of Down's syndrome in Estonia.

The aim of the study was to investigate the livebirth prevalence of Down's syndrome (DS) in Estonia during the past 14 years, create a DS database and observe the effectiveness of prenatal screening. This is a population-based descriptive study. The study subjects were children with DS diagnosis born between the years 1990 and 2003. We collected data from genetic centres in Estonia, from the databases of DS support groups, from institutions for disabled children and from the registers of family doctors/paediatricians. Prenatal screening for chromosomal anomalies for women aged >or=35 years was started in Estonia in 1995. Therefore, we divided the DS children into two groups: 112 born between 1990 and 1994 comprise group I, and 127 born between 1995 and 2003 comprise group II. Group II was further divided into two subgroups: IIa, from 1995 to 1998, when screening of advanced maternal age (>or=35 years) commenced, and IIb, from 1999 to 2003, when screening of second trimester maternal serum for younger women commenced. Prenatally, 68 cases of DS were diagnosed between 1995 and 2003 in the whole of Estonia, and all of these pregnancies were terminated. This represents 34.9% of all delivered and prenatally detected DS cases from this period. The overall livebirth prevalence was 1.17 per 1000 livebirths. The livebirth prevalence in group I was 1.25 and in group II was 1.09 per 1000 livebirths. The second trimester maternal serum screening with advanced maternal age screening was more effective than advanced maternal age screening alone. The livebirth prevalence in group IIa was 1.22 and in group IIb 0.99 per 1000 livebirths. Overall, regular trisomy was found in 90.4%, translocation in 6.3% and mosaicism in 2.9%. The overall male to female sex ratio of DS was 1.09.