Fatherhood changes a man. Parenthood is as much a turning point in life as motherhood is but mothers seem to get the larger share of the collective conversation. They also get the new wardrobe, the baby showers, and admiring smiles from strangers. Mothers also get morning sickness, unwieldy bodies, and a lifetime supply of delivery-room stories to share with other mothers. A large part of the conversation of impending motherhood is the result of hormones going on a 9-month roller-coaster ride that doesn’t come to a full stop until long after the baby’s born.

Fatherhood changes a man’s hormones, too. Studies indicate a new father’s testosterone levels drop when his child is born in what might be nature’s way of helping him to be more nurturing and accepting of his defenseless new child. The drop may enhance father-child bonding. A new study indicates a man’s hormones may change long before the baby is born; it indicates expectant fathers experience hormone fluctuations of their own as the pregnancy advances.

Dr. Robin Edelstein, an Associate Professor of Psychology in Personality and Social Contexts at the University of Michigan (UM), directs the university’s Personality, Relationships, and Hormones Lab. She and her research team wanted to know when exactly a man’s pregnancy-related hormone changes begin. They discovered paternal hormonal fluctuations begin early in the pregnancy, with peaks and valleys along the way.

Edelstein recruited 29 couples expecting their first child for the study. All study participants, ranging in age from 18 to 45, submitted as many as four saliva samples at predetermined intervals throughout the pregnancy: at weeks 12, 20, 28, and 36.

All saliva samples were tested for levels of four hormones important to pregnancy:

  • Estradiol — influences bonding and caregiving
  • Cortisol — a stress hormone
  • Progesterone — influences maternal behavior and social closeness
  • Testosterone — influences aggression and parental care

All four hormones became dramatically more abundant, as expected, in the women as the pregnancy progressed. In men, cortisol and progesterone levels stayed relatively stable during pregnancy but their estradiol and testosterone levels dropped significantly.

Edelstein’s study, one of the most extensive of its kind ever conducted, demonstrated the fluctuation of hormones other than testosterone when men face fatherhood. The study did not include a control group — a group of men of similar personal characteristics but who were not expecting their first child.

The absence of a control group leads Edelstein to note “We cannot completely rule out the possibility that the changes are simply due to age or the passage of time.”


  1. Edelstein, Robin S., et al. "Prenatal hormones in first-time expectant parents: Longitudinal changes and within-couple correlations." American Journal of Human Biology 27.1 (2015). Wiley Online Library. Web. 4 Jan. 2015.
  2. St. George, Jennifer M., and Richard J. Fletcher. "Fathers Online: Learning About Fatherhood Through the Internet." The Journal of Perinatal Education 20(3). Summer (2011): 154-62. PMC / US National Library of Medicine. Web. 3 Jan. 2015.