Born to Be a Tomboy?

Pregnancy hormones determine preschool girls' behavior, suggests study

Why do some girls love to wear dresses and play tea party while others prefer climbing trees and playing baseball?

It may have something to do with the levels of testosterone in their mother's body during pregnancy, say British researchers in a study published in the current issue of Child Development.

The higher the level of maternal testosterone, the more likely it is that girls will enjoy activities typically considered male behavior, like playing with trucks or guns, reports the study. Maternal testosterone levels don't appear to affect boys' behavior, however, according to the study.

The researchers, from City University in London, collected data on 679 children who were part of the much larger Avon Longitudinal Study of Parents and Children, which includes more than 14,000 children born in the early 1990s.

Blood samples were drawn from the mothers to look for the presence of testosterone. Twenty five percent of the mothers had blood samples taken when they were between five and seven weeks pregnant; just over half had blood drawn sometime during weeks eight through 24, and the final quarter had their blood drawn sometime after 25 weeks of pregnancy.

When the children were three and a half years old, the researchers had their mothers or primary caregivers complete a questionnaire to measure how often a child played with gender-specific toys, games or activities. Each question was scored on a five-point range of how frequently a child engages in a particular gender-specific behavior, from never to very often. Low scores on the questionnaire indicated more typically feminine behavior, while higher scores represented more male-oriented behavior. The researchers also had the children's teachers complete the questionnaire for comparison.

After controlling the data for such factors as maternal education, the presence of older siblings, a male partner living with the mother in the home, and how closely the parents followed traditional gender roles, the researchers found an association between maternal levels of testosterone and the way girls behaved at preschool age. The higher the levels of testosterone in pregnancy, the more likely girls were to score high on the questionnaire. They found no association between boys' behavior and mom's testosterone levels.

The researchers suspect there may be several reasons for this. One is that boys naturally have higher levels of testosterone prenatally and after birth, and so wouldn't be as affected by changes in maternal levels of this hormone. Another is that boys are more encouraged to behave in male gender-specific ways, and discouraged from typically female activities. For example, while many parents would be fine with their daughter playing with trucks, some parents might discourage their sons from playing with dolls.

"There's a long history of debate on the relative importance of nature or nurture [in the development of children]," says Dr. Charles Goodstein, an associate professor of psychiatry at New York University School of Medicine and the president-elect of the Psychoanalytic Association of New York.

And, he says, this study would seem to add credence to the nature side of the debate because it appears that hormone levels in the mother can affect a child's later behavior. But, he says, this study is only a beginning and that the nature vs. nurture debate will probably never be resolved.

"It's hardly ever nature or nurture. It's usually both," he says. "Simply because we inherit a genetic makeup doesn't mean our life is set in stone."

What To Do

To read more about the nature vs. nurture debate, read this article from NOVA, a Public Broadcasting Service (PBS) program. http://www.pbs.org/wgbh/nova/genome/debate.html

For more information on testosterone in women, go to DrDonnica.com. http://www.drdonnica.com/display.asp?article=3043