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The Non-Decline in U.S. Twin Birth Rates, 1964–1983
Published online by Cambridge University Press: 01 August 2014
Abstract
Detailed twin birth rates for the United States are unavailable since 1964. In 1983 the crude twinning rate for women of white race was higher than in 1964, but there had been great changes in maternal age and parity. Indirect standardization for maternal age and birth order provides estimated total twinning rates that can be compared over the entire period. The adjusted rates for whites show a nearly continuous increase except after a 2-year reporting hiatus, 1969-70, when rates dropped back 10%. In blacks the adjusted rate increased between 1966 and 1978, except for the 1968-71 shift. The distributions of rate increases by maternal age and by race argue against effects of medical ovulation stimulants, but a disproportionate increase of triplets argues for such effects. Study is needed of rates specific for maternal age and parity, rather than of total rates.
- Type
- Research Article
- Information
- Acta geneticae medicae et gemellologiae: twin research , Volume 36 , Issue 3 , July 1987 , pp. 313 - 323
- Copyright
- Copyright © The International Society for Twin Studies 1987
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