Twenty-year birth prevalence of Down syndrome in Cape Town, South Africa

The 20-year birth prevalence of Down syndrome in Cape Town South Africa was determined. All cases delivered to mothers in Cape Town plus terminations following prenatal diagnosis between 1 January 1974 and 31 December 1993 were ascertained. There were 784 Down syndrome pregnancies of which 95% were trisomies. The 32 terminations comprised 18.3% of the white 5.8% of the coloured (mixed race) and 1.4% of the black cases. The overall prevalence rate was 1.49 per 1000 (white 1.88 coloured 1.54 and black 1.29 per 1000). Analysis for linear trends showed a significant decline in rates for the total population and for whites a downward trend for coloureds but no decline for blacks. Over the last 5-year period the prevalence rates in all three population groups were 1.3 per 1000. An increasing risk with advancing maternal age was confirmed but no maternal age-specific differences in rates by race were demonstrated. (authors)