Couvade syndrome (from the French verb "to hatch") is a condition in which men go through physical changes that mimic those of their pregnant partners—and it's surprisingly common. According to a 2007 paper in the Journal of Reproductive and Infant Psychology, more than a quarter of U.S. dads-to-be report at least one symptom, including queasiness, belly-weight gain, even labor pains. Researchers have disputed whether couvade syndrome is a real medical phenomenon or, as psychotherapist Stephen Ducat, PhD, describes it, a form of "womb envy," whereby men—identifying with their wives but feeling like a sissy for doing so—"unconsciously convert their ambivalence into somatic symptoms." A 2000 study in Evolution and Human Behavior, however, found that men with couvade symptoms had lower testosterone and higher prolactin, a hormone that surges in women during pregnancy and breastfeeding. Interestingly, the same hormone pattern appeared in fathers who responded more strongly to the sound of an infant's cries in the lab. So, mothers-to-be, take heart. If your man is a nauseated, tired, moody wreck right now, his spiking prolactin might just have him changing more diapers after the baby is born.