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Decline of the Twinning Rate in Brazil

Published online by Cambridge University Press:  01 August 2014

M.H. Baena de Moraes
Affiliation:
Department of Medical Genetics, School of Medicine, UNICAMP, Campinas
B. Beiguelman*
Affiliation:
Department of Medical Genetics, School of Medicine, UNICAMP, Campinas
H. Krieger
Affiliation:
Department of Genetics, FIOCRUZ, Rio de Janeiro, Brazil
*
Dept. of Medical Genetics, Faculty of Medical Sciences UNICAMP, CP 1170, 13081 Campinas, SP, Brazil

Abstract

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The twinning rate during a twenty-year period (1965-1985) was investigated at five-year intervals in four Brazilian hospitals. During this period the twinning rate has decreased significantly (from 10.68‰ to 8.11‰), being highly negatively correlated with the five-year intervals (r = −0.97). This change was due mainly to the decline in dizygotic twinning, since the incidence of DZ twins has fallen from around 7‰ in 1965 to around 3.6‰ in 1985. The detected decline in DZ twinning seems to be due to the remotion of the fertility advantage of the more fecundable DZ twin-prone women by the introduction of effective birth control at the present, while some other mechanisms are causing the decline irrespective of the type of twinning.

Type
Research Article
Copyright
Copyright © The International Society for Twin Studies 1989

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