How to survive a new baby without destroying your marriage, according to a relationship psychologist and father of two

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Eli Finkel's take on parenting is perhaps best summed up in his description of his baby as a "puking piece of adorableness."

Time was, he or his wife would want to spend the night out with friends; the other would send them off, no problem. Once their baby arrived and his wife would go out, Finkel said, he would now be solely responsible for this, well, puking piece of adorableness.

Finkel is a psychologist at Northwestern University and a professor at the Kellogg School of Management. In his new book, "The All-or-Nothing Marriage," Finkel both explains why modern marriage is so hard and offers some guidelines for strengthening your own relationship.

In one section, he describes how parenting can take a toll on a marriage, and admits that he was one of the 25% of men who suffer from postpartum depression. When he visited the Business Insider office in September, he said he was surprised — and somewhat dismayed — by how much having a kid changed his life.

To expectant parents, or to people who hope to one day have kids, he said the key to survival is adjusting your expectations.

Here's how Finkel described his own experience: "I just felt like everything that I had enjoyed doing in my life was gone, and replaced with a lack of sleep. I did love my child of course, but the way that it affected my life was depressing for me."

Finkel's personal experience affected his marriage, putting some distance between him and his wife. It took a while for them to reestablish intimacy. Adjusting their expectations helped.

In the book, Finkel describes a post-baby vacation with his wife that wasn't nearly as enjoyable as it used to be. On that trip, they decided to stop shooting for the stars. He writes:

"Seeking bliss through the marriage — particularly looking to each other for assistance with personal growth and self-expression — just made things worse. So we just stopped trying. We put our heads down and focused on putting one foot in front of the other.

"That approach worked. The disappointment became less acute. And, eventually, we rediscovered each other."

By the time he and his wife had a second kid, Finkel told Business Insider, he and his wife had "recalibrated":

"Both of us understood that this isn't going to be the time when we're going to enjoy each other in the marriage the way we used to. This isn't going to be the time when our spouse is going to be as attentive to us and as responsive. This isn't going to be a time when we're really going to have that much alone, well-rested time together. And how disappointed are we going to be about that?"

The transition to having a second baby went much more smoothly.

Other scientists have studied the transition to parenting, and the "buffers" that protect against a decline in marital satisfaction. According to Alyson Fearnely Shapiro, then at the University of Washington, two of those buffers are "being aware of what is going on in your spouse's life and being responsive to it" and "approaching problems as something you and you partner can control and solve together as a couple."

The takeaway here is that you can never fully prepare for having a kid — but you can prepare for your life to change in some capacity, and you can talk to your partner about how you'll each help each other through the low points.

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