Maternal age-specific risk of Down syndrome in an Asian population: a report of the Taiwan Down Syndrome Screening Group.

This study is a novel approach in establishing the maternal age-specific risk for Down syndrome screening in an Asian population. The relative frequency by one-year maternal age interval in women who had live births in the Taiwan area between 1975 and 1995 was used as the age-specific distribution of women who had unaffected pregnancies. Data about Down syndrome live births were obtained from the Taiwan Down Syndrome Association to establish the age distribution of women who had Down syndrome live births. The relative frequencies and the likelihood ratio by one-year maternal age interval was calculated and smoothed by running median and moving average smoothing methods. The age-specific risk was established by multiplying the total population risk by the likelihood ratio of the specific maternal age. The total live births in the Taiwan area between 1975 and 1995 were 7,232,689. A total of 527 cases of Down syndrome live births were registered in the Taiwan Down Syndrome Association. A total of 466 cases (88.43 per cent) of Down syndrome live births occurred before age 35, which was higher than occidental reports. This study established the first sizeable database of maternal age-specific risk for Down syndrome in an Asian population.