ON A RECENT SUNDAY, my wife, Jill, woke with a start at 3 a.m. Propped up on one elbow and looking grim, she said, “I want another child.” And that made me nervous.

I’m not opposed to more children. It’s just that getting pregnant, for us, has always been about a lot more than a perfectly timed romp in the hay. See, about 10 percent of American couples are hampered by infertility. The US Department of Health and Human Services Office on Women’s Health defines the condition as “not being able to get pregnant after one year of trying (or six months if a woman is 35 or older).” The label can also apply to “women who can get pregnant but are unable to stay pregnant.” Six million-plus American women fall into at least one of those categories.