Letters

The fragile male

BMJ 2001; 322 doi: https://doi.org/10.1136/bmj.322.7286.617/a (Published 10 March 2001) Cite this as: BMJ 2001;322:617

Male zygotes are often formed at suboptimal times in fertile cycle

  1. William H James, honorary research fellow
  1. Galton Laboratory, University College London, London NW1 2HE
  2. Men's Health Forum, London WC1H 9JP

    EDITOR—Kraemer adduced large quantities of data to substantiate the proposition that, from conception, males are more vulnerable than females.1 Postnatal vulnerability has some social causes, which are known, but the causes of the prenatal vulnerability of males are not established, so I wish to suggest one.

    During the menstrual cycle women have a fertile window lasting several days.2 There is strong direct3 and indirect4 evidence that the regression of the sex ratio of the offspring (proportion male) on the time of fertilisation is …

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