“Dads have doubled the amount of time they spend in childcare from 1965 to 2011,” says Dr. Craig Garfield, lead author on the study and associate professor in pediatrics hospital-based medicine and medical social sciences at Northwestern. “If we know that dads who are depressed are more likely to use physical punishment and less likely to read to their kids, this has an effect on the child as well…Dads are key players. They have contributions to make, and they can be positive or negative contributions.”

Postpartum depression may be more likely to go undiagnosed in men, though, as men are traditionally less likely to ask for help than women, and are more willing to report problems like irritability and fatigue than feelings of sadness or worthlessness.

“I’m not sure that the male/female part has as much to do with it as we all thought,” says Karen Kleiman, founder and director of the Postpartum Stress Center and author of This Wasn’t What I Expected: Overcoming Postpartum Depression. “It’s just hard to have a baby. It’s hard to have a baby and continue to work, at work and at your relationships.”

Intellectually, most of us know this. That having a baby changes everything is stale, cliché—if true—advice. But there’s a difference between knowing and doing, and even parents who are prepared and eager to have a child can easily find themselves overwhelmed during the transition. Whether that will translate into depression for a particular person is impossible to predict, but stems from an elusive combination of genetics, psychology, and the support available to the parent.

One thing that seems to play into all this is the dissonance between a person’s expectations of parenthood and the reality.

“It’s like holding your breath for a really long time,” Kleiman says. “Then all of a sudden we get what we think we want and think, ‘I finally have what I want, why do I feel so bad? And now on top of that I feel guilty for feeling so bad.’”

Unmet expectations play a particularly key role in the development of depression in adoptive patients, according to Dr. Karen Foli, an assistant professor at the Purdue University School of Nursing and author of The Post-Adoption Blues. “The adoptive process is a pretty rigorous investigation,” she says. “The adoptive parent is kind of selling themselves as being worthy of a license to parent. After the placement of the child, no parent can uphold that.”

No parent can be that kind of super-parent all the time, just as no child can be the perfect child parents may build up in their heads while waiting to adopt. Many adopted children may come to their new homes with challenging behaviors, depending on their pasts. Adoptive mothers Foli studied were more likely to experience depressive symptoms if they reported having expectations of themselves, the child, or family and friends. Foli says the rate of depression is similar in adoptive mothers and birth mothers—around 7 to 8 percent. (The Centers for Disease Control and Prevention put the rate at 8 to 19 percent for birth mothers, and about 4 percent for fathers).