Temporal increase in the rate of Down syndrome livebirths to older mothers in New York State.

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Abstract
In New York State [USA] exclusive of New York City, the standardized rate of Down''s syndrome in livebirths to women 35 and over reported on birth certificates increased 30% in 1970 and later years, compared to the rate in 1965 and 1969. In contrast, there was no change in those under 35. A separate investigation revealed that selective temporal differences in reporting of cases born to older mothers did not account for the change. A similar increase in rates of cases born to older, but not younger, mothers in 1970 and later years has also been reported from Manitoba [Canada]. These observations may be pertinent to apparent discrepancies between livebirth rates of Down''s syndrome and those reported at amniocentesis.