A study of the sex ratio of first-born According to the mother's month of birth
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- Miura, T., Nonaka, K., Shimura, M. et al. Arch. Gynecol. (1983) 233: 263. doi:10.1007/BF02133800
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The male-to-female sex ratio at birth of the first-born babies delivered in Japan to mothers aged 25 years or less was investigated in two groups: a hospital group and a questionnaire group. The sex ratio fluctuated according to their mother's month of birth. Between 1924 and 1928, the sex ratio of the offspring of the mothers born in March-May in both groups was significantly higher than that of the other mothers. We speculate about the relationship between the sex ratio at birth and the mother's month of birth.