Results of first year (1989) of a national register of Down's syndrome in England and Wales.

Objective: To examine the feasibility of a national register of Down's syndrome and its effectiveness in evaluating prenatal screening for the syndrome.
Design: Information for the register was obtained from all eligible cytogenetic laboratories on relevant cytogenetic diagnoses, including date and place of birth or termination, maternal age, indication for karyotyping, and type of diagnostic test used.
Setting: Cytogenetic laboratories in England and Wales.
Subjects: All fetuses with trisomy 21 diagnosed prenatally and live births with Down's syndrome diagnosed at birth.
Main Outcome Measures: Number of prenatal and postnatal diagnoses of Down's syndrome. National and maternal age specific prevalence of Down's syndrome.
Results: For 1989 there were 1060 registrations--323 prenatal diagnoses and 737 postnatal diagnoses--after exclusion of postnatally diagnosed miscarriages and stillbirths. The estimated national rate of affected births for mothers resident in England and Wales was 1.4/1000 live births, assuming no terminations of affected pregnancies and after correction for natural losses which would have occurred in the absence of termination. The corrected maternal age specific rates were close to those found in previous population based studies. The proportion of affected pregnancies diagnosed prenatally in mothers aged 35 to 39 was 44%, and for those aged 40 or more it was 71%. Abnormal findings on ultrasonography played an unexpectedly important part in initiating cytogenetic investigation (13% of the prenatal diagnoses).
Conclusions: The findings establish the feasibility of a national Down's syndrome register and its use in evaluating prenatal screening services. Together with information held by the Office of Population Censuses and Surveys on congenital malformations, data from the register will permit studies of environmental variables affecting the prevalence of the syndrome.