Brief reports decline of Down's syndrome after abortion reform in New York State

Abstract

Incidence rates derived from prospective studies of 120,000 newborns were applied to live births and induced abortions in order to estimate the trend of Down's syndrome in New York State after liberalization of the abortion law in 1970. Women aged 35 years of older, at higher risk of Down's syndrome births, sought terminations of their pregnancies more frequently than did younger women. The estimated number of newborns with Down's syndrome in the state declined 20 percent from 1971 to 1975. In New York City, more pregnancies in the high-risk age range were aborted than were carried to term. These trends indicate that abortion reform may have made a significant contribution to the reduction of severe mental retardation.

PIP: The report estimates the impact of the 1970 abortion reform on the occurrance of Down's syndrome in New York State. The New York legislature removed restrictions on induced abortions during the first 2 trimesters of pregnancy. The sources of data were: 1) 2 series of newborns from the WHO Comparative Study of Congenital Malformations, 2) Jerusalem Perinatal study, and 3) 2 series from the U.S. Colaborative Perinatal Project. The maternal age-specific incidence from the 5 data sources were applied to the number of pregnancies in each maternal age group supplied by the New York State and City Departments of Health. In 1968 and 1969 the number of expected cases remained stable (383 and 379, respectively), and following the 1970 abortion reform the expected frequency dropped from 331 cases in 1971 and 293 cases in 1972. The decline in incidence of Down's syndrome was attributable to an increase of induced abortions rather than a decrease of pregnancies, especially in New York City and in the older maternal age groups (35 or older). In the 5 years after abortion reform, the proportion of pregnancies terminated rose during the first 3 years and then stabilized. In the same time period, the estimated number of births with Down's syndrome declined by 20 percent. The decline in Down's syndome in New York State cannot be attributed entirely to the abortion reform, although the abortion reform was effective in reducing the incidence of severe mental retardation.