Evolución secular y por comunidades autónomas de la frecuencia de síndrome de Down al nacimiento en hijos de madres jóvenes

Abstract

Introduction There is a universally proven relationship between maternal age and the risk of having an infant with Down syndrome (DS); the risk is greater as maternal age increases. The overall risk is increased almost 10-fold in mothers aged more than 34 years (traditionally accounting for 9-14% of all mothers) than in those aged less than 35 years. For this reason, mothers aged 35 years or older have constituted the target population for prenatal diagnosis of DS and, consequently, the frequency of newborn infants with DS in this age group has clearly decreased over time. However, the development of new prenatal screening techniques has allowed groups with a higher risk to be detected among young mothers. The aim of this study was to analyze trends in the frequency of DS in the infants of mothers aged less than 35 years old in Spain over the last 28 years by autonomous communities in Spain. Material and methods Data from the Spanish Collaborative Study of Congenital Malformations (Estudio Colaborativo Español de Malformaciones Congénitas [ECEMC]) corresponding to the period 1976-2003, and obtained from all the autonomous communities in Spain, were used. The ECEMC is a clinical-epidemiological research program on the causes of congenital defects, structured as a permanent registration system with a case-control design. The program is hospital-based. For the analysis of time trends, the lineal trend test (χ2 with 1 degree of freedom) was used. To detect deviations from linearity, a χ2 test with k-2 degrees of freedom was used. Results The overall frequency of DS in mothers younger than 35 years significantly decreased over time (p = 0.03), mainly in the last few years. This decrease was statistically significant in the autonomous communities of Catalonia (p = 0.002) and Galicia (p = 0.01), but was nonsignificant in Andalusia, Balearic Island, Madrid and the Basque Country. In Navarre and La Rioja, the most recent tendency could not be evaluated because these regions temporarily interrupted their participation in the study. A statistically significant increase was found in the Principality of Asturias. No notable tendencies were found in the remaining regions.The percentage of mothers older than 34 years progressively increased, accounting for 20.54% of all mothers in 2003, while the number and percentage of infants with DS born to mothers older than 34 decreased and was lower those of infants with DS born to mothers younger than 35 years. Discussion Although the time trend of the frequency of DS in the infants of mothers aged less than 35 years showed a significant overall