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Twinning Rate by Month of Mother's Birth in Japan

Published online by Cambridge University Press:  01 August 2014

T. Miura*
Affiliation:
Department of Hygiene, Teikyo University School of Medicine, Tokyo
I. Nakamura
Affiliation:
Department of Hygiene, Teikyo University School of Medicine, Tokyo
M. Shimura
Affiliation:
Department of Hygiene, Teikyo University School of Medicine, Tokyo
K. Nonaka
Affiliation:
Department of Hygiene, Teikyo University School of Medicine, Tokyo
Y. Amau
Affiliation:
The Japanese Association of Twins' Mothers, Tokyo
*
Department of Hygiene, Teikyo University School of Medicine, Kaga, Itabashi-ku, Tokyo 173, Japan

Abstract

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Records of two hospitals and of an association of mothers of twins were analysed for the years 1924-1980, finding a total of 656,109 and 1185 twin births, respectively. Twinning rates were higher in summer or fall, in general, but these seasonal variations occasionally changed within a short period of years, as in 1973-75 in the Association group. The twinning rate was also affected by the month of mother's birth. It was low among the mothers born around May-July in maternities up to 1960, and these mothers did not show seasonal variation of twin births. The unlike-sexed twinning rate of the mothers born in May-July was also lower than that of the other mothers, and constantly low even at higher maternal ages. A possible explanation for these phenomena is discussed.

Type
Research Article
Copyright
Copyright © The International Society for Twin Studies 1984

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