title: Investigation on seasonality of twin births in Brazil.
abstract: The hypothesis of seasonality of twin births was investigated in two important maternity hospitals in the State of São Paulo, Brazil. The study included 1,386 twin births that occurred among 154,699 deliveries from 1984 to 1993. No evidence of seasonality has been detected either for the twin birth rate considered as a whole or for dizygotic twinning rate. The distributions of these rates fitted well sinusoidal regression curves but the cyclic trend did not correspond to any specific season.
authors.affiliation: Department of Parasitology, University of São Paulo, Brazil.
authors.forename: H
authors.initials: H
authors.lastname: Krieger
authors.forename: G M
authors.initials: GM
authors.lastname: Colletto
authors.forename: C
authors.initials: C
authors.lastname: Franchi-Pinto
authors.forename: B
authors.initials: B
authors.lastname: Beiguelman
mesh_terms: D000704:Analysis of Variance; D001938:Brazil; D005260:Female; D006801:Humans; D015994:Incidence; D007231:Infant, Newborn; D011247:Pregnancy; D011272:Pregnancy, Multiple / Q000706:statistics & numerical data*; D012621:Seasons; D014427:Twins / Q000706:statistics & numerical data*; D014429:Twins, Dizygotic / Q000706:statistics & numerical data