Testosterone levels synchronise more in new parents who have a strong commitment to their relationship

Photo: Jc Olivera. Creative Commons.

If a father is more committed to the relationship with the mother, I found that his testosterone drops more.

Testosterone drops when men become fathers (see Testosterone changes in caring men), which may reflect a shift in the new father’s priorities away from competing for new mates and towards caring for an infant.

If a father is more committed to the relationship with the mother after the birth of his child, we found that his testosterone drops more, and he shows stronger correlations with his partner’s testosterone across pregnancy.

I collaborated with Robin Edelstein, a researcher at the University of Michigan who has studied hormonal changes in couples expecting their first child. Over several months, Dr. Edelstein collected samples of testosterone and other hormones from both pregnant women and their partners. Couples came into the lab four times, spanning early to late pregnancy. Dr. Edelstein also surveyed couples a few months after their baby’s birth to ask about their relationship and parenting experiences.

She and I tested how fathers’ testosterone levels changed across pregnancy, and also whether fathers’ and mothers’ testosterone levels were correlated with each other. We found that the fathers who showed more of a drop in testosterone over pregnancy reported being more invested, committed, and satisfied in their relationships with their partners after their baby’s birth. Fathers also reported more dedication to the postpartum relationship if they showed more synchrony in testosterone with their partners. In other words, fathers whose testosterone correlated more highly with their partner’s at each of the four pregnancy visits were more likely to endorse a stronger level of investment in the partner relationship after birth. These results suggest that fathers’ dynamic changes in testosterone over pregnancy may indeed reflect their intimate relationship priorities during the transition to parenthood.

Women’s testosterone rises in late pregnancy, due to the influence of the placenta. In other words, men and women may show the opposite pattern of testosterone change across pregnancy. However, partners may still have correlated levels of testosterone at each visit. By using a statistical model that included both the influence of time (number of weeks into the pregnancy) and the partner’s hormone level, we were able to test both change across pregnancy and the level of synchrony within the couple.

Although I have found in several studies that cortisol synchrony appears in more distressed relationships, in this case, more correlated testosterone predicted more postpartum commitment. These differences may be due to the different function of these hormones – one plays a role in stress, the other in reproduction.

In order to understand these and other processes better, I’m currently collecting data for the HATCH (Hormones Across the Transition to Childrearing) study, a new study that will follow couples from pregnancy across the first year of parenthood, and will sample both cortisol and testosterone from mothers and fathers. I’m hoping to again look at synchrony within couples and whether it predicts family well-being over a sensitive period like the transition to parenthood.

Studying the physiology of families can help us understand how families operate and what kinds of family dynamics either promote or dampen health.