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Annual Variation of Sex Ratio in Twin Births and in Singletons in Brazil

Published online by Cambridge University Press:  01 August 2014

B. Beiguelman*
Affiliation:
Department of Medical Genetics, School of Medicine, UNICAMP, Campinas, SP, Brazil
C. Franchi-Pinto
Affiliation:
Department of Medical Genetics, School of Medicine, UNICAMP, Campinas, SP, Brazil
G. M. D. Dal Colletto
Affiliation:
Department of Parasitology, University of S. Paulo, S. Paulo, SP, Brazil
H. Krieger
Affiliation:
Department of Parasitology, University of S. Paulo, S. Paulo, SP, Brazil
*
Departamento de Genética Médica, Faculdade de Ciências Médicas, C.P. 6111, UNICAMP. 13081-970 Campinas, SP, Brazil

Abstract

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The annual variation of the sex ratio (SR) of 1385 twin births was analyzed and compared to that of 85909 singletons. These births referred not only to live births but also to stillbirths in two southeastern Brazilian maternity hospitals from 1984 to 1993. While the annual variation of the SR of singletons was very small, that of twin births was extremely high, due to the significant heterogeneity of the annual data. It is suggested that the large SR annual variation of the twin birth might be a consequence of the variation of male or female monozygotic twins.The hypothesis that twin births show a lower sex ratio than singletons could not be supported by the present data.

Type
Research Article
Copyright
Copyright © The International Society for Twin Studies 1995

References

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