Factors affecting the incidence of Down syndrome in Scotland

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Abstract
Summary: The incidence of Down syndrome in Scotland between 1960 and 1974 was estimated using data from thirteen Area Health Boards. Incidences in individual years, in different months of the year and in different maternal age groups were also determined. There was an apparent increase in incidence in more recent years almost certainly due to increased ascertainment. This may have obscured any decrease in incidence which might be expected as a result of a decrease in mean maternal age during this period and the introduction of antenatal diagnosis. No seasonal differences in incidence could be detected either in the whole area or in individual Area Health Boards. There was an increase in incidence with maternal age which was not significantly different from that found by other investigators. There was also an indication of an increase in relative incidence (% Down syndrome births/% live births) over the period 1966–74 in mothers aged 35 years and older.