Exposure to Phthalates

Swan and her colleagues tested urine samples of 74 pregnant women who gave birth to boys and 71 who gave birth to girls, looking for nine different phthalates. The women were part of The Study for Future Families, an ongoing study.

When the children were ages 3.6 to 6.4 years, Swan's team asked the mothers to answer questions about their children's play behavior. Parents described the type of toys and play their children favored, and each child was given a score reflecting masculine-typical play or feminine-typical play.

Exposure to two of the nine phthalates, DEHP and DBP, was associated with less masculine play behavior, the researchers found.

For example, Swan says, ''If the mother's MEHHP concentration [one of the phthalate metabolites] was high, in the upper quartile, the odds that her boy had a score that was less masculine [in play behavior] was five times greater than mothers whose MEHHP was in the lowest quartile."

Exposure to phthalates may lower testosterone production in the fetus during a crucial period of development, at about 8 to 24 weeks' gestation, Swan says, when the testes begin to function, and in doing so alter sexual differentiation in the brain.