EPIDEMIOLOGY OF DOWNS-SYNDROME IN A SCOTTISH CITY

The aim of the study was to investigate aspects of the epidemiology of Down's syndrome (DS) in a population subjected to continuous surveill ance. Data were obtained from the Glasgow Register of Congenital Anoma lies. Over the period 1980-90, 173 cases of DS were identified (1.2 pe r 1000 births), of which 135 (78.1%) were livebirths, five (2.9%) were stillbirths and 33 (19.1%) were terminations following prenatal diagn osis. The increasing risk of DS with advancing maternal age was confir med, although most DS pregnancies occurred in women aged under 35. Whi le the birth prevalence of DS did not vary significantly over time, th ere was a significant increase in DS pregnancy prevalence. The proport ion of all DS pregnancies terminated showed a statistically significan t rise from 14% in 1980-87 to 31% in 1988-90 following the introductio n of a new screening marker for DS risk. Almost half of DS pregnancies in women aged 35 and over ended in termination following prenatal dia gnosis compared with only 7% in women under 35. There was a statistica lly significant excess risk of DS pregnancy in the more prosperous are as of the city; this excess persisted, but was not statistically signi ficant, after standardising the rates for maternal age. These findings suggest that there is no scope for reducing service provision for DS children on the basis of the epidemiological trends, that the antenata l screening programme, while benefiting from the recent introduction o f serum markers of risk, continues to have a greater impact on older w omen, and that further aetiological research using population based re gistries is required.