Till Children Do Us Part By STEPHANIE COONTZ Olympia, Wash. HALF a century ago, the conventional wisdom was that having a child was the surest way to build a happy marriage. Womens magazines of that era promised that almost any marital problem could be resolved by embarking on parenthood. Once a child arrives, we dont worry about this couple any more, an editor at Better Homes and Gardens enthused in 1944. There are three in that family now. ... Perhaps there is not much more needed in a recipe for happiness. Over the past two decades, however, many researchers have concluded that threes a crowd when it comes to marital satisfaction. More than 25 separate studies have established that marital quality drops, often quite steeply, after the transition to parenthood. And forget the empty nest syndrome: when the children leave home, couples report an increase in marital happiness. But does the arrival of children doom couples to a less satisfying marriage? Not necessarily. Two researchers at the University of California at Berkeley, Philip and Carolyn Cowan, report in a forthcoming briefing paper for the Council on Contemporary Families that most studies finding a large drop in marital quality after childbirth do not consider the very different routes that couples travel toward parenthood.