title: Decline of the twinning rate in Brazil.
abstract: 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.
authors.affiliation: Department of Medical Genetics, School of Medicine, UNICAMP, Campinas.
authors.forename: M H
authors.initials: MH
authors.lastname: Baena de Moraes
authors.forename: B
authors.initials: B
authors.lastname: Beiguelman
authors.forename: H
authors.initials: H
authors.lastname: Krieger
mesh_terms: D001938:Brazil / Q000453:epidemiology; D004813:Epidemiology; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D008423:Maternal Age; D010298:Parity; D011247:Pregnancy; D011272:Pregnancy, Multiple