Justification:

Down syndrome is the most frequent chromosomopathy in Costa Rica and the world, as well as the main cause of intellectual disability. Advanced maternal age is the main known risk factor for this condition. The objective was to know the trend of Down syndrome in live births according to maternal age in Costa Rica.

Methods:

A prevalence study was made of all Down syndrome cases, born alive in Costa Rica from 1996 to 2016 and reported to the Costa Rican Births Defects Register Center, a national program for the monitoring of congenital defects. The trend and prevalence in live births was determined, according to maternal age: <20, 20-34 and 35 years or more, and according to period: 1996-2007 and 2008-2016. A Poisson regression was carried out, taking as references the group 20-34 years and the period 1996-2002 and the results were compared Wald’s chi-square. The prevalence ratio in mothers ≥35 years and the population attributable fraction was calculated for this stratum. Finally, the trend of Down syndrome was compared with the trend of the specific fertility rate in mothers ≥35 years.

Results:

For 1996-2016 the prevalence of Down syndrome in live births was 1.02 x 1000 (95% CI: 0.97-1.07). There was a significant increase from 0.91 (1996-2007) to 1.16 x 1000 (2008-2016), at the expense of the prevalence in mothers ≥35 years, which increased from 4.27 to 5.44 x 1000; while the fertility rate in these mothers fell significantly from 20.15 x 1000 (95% CI: 20.02-20.28) in 1996-2007, to 15.58 x 1000 (95% CI 15.46-15.70) in 2008-2016. Maternal age mean MS in SD was 32.2 years, versus 25.5 years in the general population (p≤0.001). The prevalence ratio adjusted by period, in mothers of ≥35 years, against mothers of 20-34 years was of 8.05 (95% CI 7.25-8.95) and the population attributable fraction was 41.22%.

Conclusions:

The livebirth`s prevalence of Down syndrome in Costa Rica increased for the study period, at the expense of prevalence in mothers ≥35 years, although the specific fertility rate in these women fell significantly. The inclusion of the National Children’s Hospital - as a national reference institution for this syndrome - within the surveillance network of congenital defects, could be a determining factor in in prevalence rise.