Researchers have found for some time that marital satisfaction drops when the kids are born. Couples need to have a strong marriage to survive the family crisis of having a baby. Nearly all marriages that do handle the crisis are stronger and ultimately happier for it. The great majority of parents find their own lives more meaningful for having kids.
Philip and Carolyn Cowan, longtime family researchers at Berkeley, recently parsed what happens to marital happiness for different kinds of parents. Couples who did not plan to have kids, were ambivalent about it, or disagreed about having children were less happy than they had been before. The account for almost all of the overall drop in marital satisfaction that married couples as a whole report when they have kids.
By contrast, parents who planned to have kids or who welcomed a somewhat surprising conception remained happy, and sometimes got happier, when they had a baby.