Sex makes babies. So it is ironic that the child, the embodiment of the couple's love, so often threatens the very romance that brought that child into being. Sex, which set the entire enterprise in motion, is often abandoned once children enter the picture. Why does parenthood so often deliver such a fatal blow?

The transition from two to three is one of the most profound challenges a couple will ever face. It takes time--time measured in years, not weeks--to find our bearings in this brave new world. Having a baby is a psychological revolution that changes our relation to almost everything and everyone. Priorities shift, roles are redefined, and the balance between freedom and responsibility undergoes a massive overhaul.

Eventually, most of us come to recognize ourselves again within this new context of family. For some of us, this is when romance starts to work its way back into the fabric of our lives. We remember that sex is fun; it makes us feel good, and it makes us feel closer.

But while some couples gravitate toward each other again, others slowly wander off on a path of mutual estrangement. Reclaiming erotic intimacy is not always easy. The case is often made that American parents today, regardless of class, are overworked and overwhelmed. We constantly sort conflicting demands into their appropriate hierarchical slots: The Crucial, The Important, The Dreamt of, The Ought-to. Sex often remains firmly at the bottom of the "to do" list, never…