Down's syndrome in South Africa - incidence, maternal age and utilisation of prenatal diagnosis
Down's syndrome (DS) is the most common chromosomal cause of mental retardation, and amniocentesis is the most significant factor affecting its prevalence. In South Africa, prenatal cytogenetic diagnoses have been available for just over a decade and the utilisation and effect of this procedure in the white population born between 1980 and 1984 was evaluated. On the basis of pooled data involving 4939640 births, an overall world mean rate for DS of 1,34/1000 live births (mainly Caucasian) for single-year maternal ages was calculated. Accordingly, 58 cases of DS were expected in the 40 year and older maternal age group in South Africa. Only 34 cases (59%) were detected prenatally, and a further 3 cases were identified by the notification system during the same period and in the same maternal age group. Another 24 DS cases in the maternal age group of 40 years and over could thus potentially have been detected prenatally and prevented, while 21 cases in this age group (36%) could not be accounted for at all. Cost-benefit analyses are shown and the number of amniocenteses required for various maternal age groups to affect the prevention of DS is calculated.