Among lesbian couples expecting their first child, low prenatal testosterone levels predict a higher quality of nurturing behavior, according to a new University of Michigan study.

People tend to associate the hormone testosterone with males, competition and dominance. But women also have testosterone and it is also associated with caregiving and nurturance.

However, the majority of testosterone research focuses on heterosexual samples, which limits our understanding of how these findings generalize to nonheterosexual people, says Kristi Chin, a U-M psychology graduate student and the study’s lead author.

Twenty-five lesbian couples between ages 18 and 45 provided saliva samples to measure testosterone each trimester during pregnancy and completed a questionnaire three months after their scheduled due date. The questionnaire assessed spousal support, division of household labor and infant care, parenting behaviors and relationship quality.

Chin and colleagues found that—for both partners—lower testosterone during pregnancy predicted better relationship quality and more time spent taking care of the baby.

Relationship quality and parenting behavior also depended on the partner’s testosterone levels: Mothers were more committed to partners and more overprotective of children when their partner’s testosterone was lower.

“Our findings contribute important new knowledge about the functionality of testosterone in close relationships contexts, including some of the first evidence among sexual minorities,” Chin said.

The results of the study, she says, are consistent with prior work involving expectant heterosexual couples, which suggests that lower testosterone levels promotes greater caregiving and nurturance.

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