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Related Experiment Videos

Gender mix: does it modify birthweight--outcome association?

Robert Derom1, Catherine Derom, Ruth J F Loos

  • 1Association for Scientific Research in Multiple Births, Destelbergen, Belgium. Robert.derom@pandora.be

Paediatric and Perinatal Epidemiology
|January 27, 2005
PubMed
Summary

In male-female twins, the female twin slightly increases her male co-twin's birthweight. Conversely, a female twin's higher birthweight than her male co-twin is linked to improved cognitive development (IQ).

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Area of Science:

  • Reproductive biology
  • Human development
  • Twin studies

Background:

  • The phenomenon of "gender mix" in utero, particularly potential hormone transfer between male and female co-twins, is controversial in humans.
  • While observed in animals (e.g., free-martin syndrome in cattle), convincing evidence in humans remains elusive.

Purpose of the Study:

  • To investigate the effects of gender mix on birthweight and cognitive development in human twins.
  • To analyze data from the East Flanders Prospective Twin Survey, a large population-based registry.

Main Methods:

  • Utilized data from the East Flanders Prospective Twin Survey, including pregnancy details, placental structure, and zygosity.
  • Examined birthweights and cognitive development (IQ scores from WISC-R) in relation to co-twin sex and birthweight differentials.

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Main Results:

  • Female twins' birthweights are not affected by a male co-twin.
  • Female twins unexpectedly enhance the birthweight of their male co-twins by slightly prolonging gestation.
  • Female twins with higher birthweights than their male co-twins show increased cognitive development (IQ) compared to controls.

Conclusions:

  • Human twins exhibit subtle sex-specific influences on birthweight and cognitive development.
  • Female fetuses may positively influence male co-twin birthweight, while relative birthweight impacts female cognitive outcomes.