The prevalence of Down’s syndrome and maternal age in central Dalmatia

This paper presents data from an epidemiological surveillance of Down’s syndrome (trisomy 21) in the region of Central Dalmatia. The prevalence of trisomy 21 in the period from 1988-1992 in relation to various maternal ages as well as in the mean population, disregarding the parents' ages, was 12.9:10000 or 1:775, which is very close to the mean rate of prevalence of the Central EUROCAT Registry: 11.85:10000 or 1:884 among live births and stillbirths. The observed differences, for example the higher prevalence in the mean population - 14.5:10000 (1980-1992);17.2:10000(1990-1999), and also the lower occurrence of Down’s syndrome in the 30 years and older age-group among the EUROCAT population, can be attributed to the discrepancies in prenatal diagnosis (PND) of trisomy 21, followed by pregnancy termination. Among our participants, not a single case of PND of trisomy 21 resulting in pregnancy termination was found, while more than 20 per cent of total number of registered trisomies 21 in EUROCAT registries account for such cases, which are all included in the mean prevalence of this chromosomal abnormality- hence the differences. It is established that trisomy 21 is more often detected at an earlier gestational age, with a considerable percentage being spontaneously aborted before 22 weeks gestation. All participants in this paper had free type trisomy 21, whose occurrence is closely linked to maternal age. Due to this fact, for successful prevention of DS, besides prenatal diagnosis and pregnancy termination, it is of utmost importance to educate and encourage would-be parents to start families earlier in the reproductive period, preferably by the age of 35, in order to decrease the risk of having a child affected with Down’s syndrome, burdened with numerous health and other problems.