Levels of the sex hormone, testosterone, in the mother’s blood during pregnancy predict how girls behave at pre-school age, a study has found.
Researchers at City of London and Bristol Universities have found that mothers of girls who were extremely feminine in their behaviour had the lowest levels of testosterone in their blood during pregnancy, and mothers of girls who were extremely masculine had the highest levels. The mothers of girls who showed conventionally feminine behaviour had intermediate levels of testosterone during pregnancy. Boys were also tested, but the mother’s testosterone levels did not apparently relate to the way they behaved.
Those studied were all part of the Children of the 90s, also known as the Avon Longitudinal Study of Parents and Children, the largest population study of its kind, based at Bristol University. They had been followed since week 20 of gestation.
Researchers at City University took answers given in questionnaires by the parents on their child’s play with sex-typical toys, games and activities when the child was three and a half years old. They measured the testosterone in blood samples that had been obtained during pregnancy from the mothers of the children.
Six groups were studied: extremely feminine girls, extremely feminine boys, extremely masculine girls, extremely masculine boys and two randomly selected groups, in all the testosterone levels of the mothers of nearly 700 children were examined.
Other factors that could influence gender-typical behaviour were also assessed, such as the number of older brothers or sisters in the home, parental compliance with traditional sex-roles, the presence of a male partner in the home and levels of education in the mother. However, the researchers found that these factors did not account for the relationship they saw between testosterone and behaviour in the pre-school girls.
Sex hormones in pregnancy influence play behaviour in non-human primates. Other studies have suggested that they may also influence the development of human behaviour. For example, girls who experience higher than normal levels of testosterone and other androgens in the womb because of a genetic disorder, show more masculine-typical play behaviour.
The lead researcher, Professor Melissa Hines, wanted to know if normal variability in levels of testosterone in pregnancy would also influence how a child later plays.
She concludes that, “Our results suggest that this hormonal influence may also apply to normal human development, and that hormonal influences on brain development and behaviour that have been documented in other species apply to some extent to humans as well.”
Notes
Hines M, Golombok S, Rust J, Johnston KJ, Golding J, ALSPAC Study Team. "Testosterone during pregnancy and gender role behaviour of pre-school children: A longitudinal, population study." Child Development. doi: 10.1111/1467-8624.00498
ALSPAC The Avon Longitudinal Study of Parents and Children (also known as Children of the 90s) is a unique ongoing research project based in the University of Bristol. It enrolled 14,000 mothers during pregnancy in 1991-2 and has followed most of the children and parents in minute detail ever since.