Imagine for a moment this perfectly plausible scenario: You've had a steady girlfriend for a year or so and everything's going great. You still hold hands at the movies. Friends tell you you're good together. You're both around 30 years old and making plenty of money, maybe living together, but you're nowhere near considering fatherhood. And though you occasionally get the feeling that her biological clock is set far ahead of yours, she tells you she's "safe," so you don't worry. Why would you? It's not as if you'd just picked her up on Dollar Margarita Night at Senor Frog's. But one morning she tells you something has gone wrong. Unlikely as it sounds, she's pregnant-and she wants to keep it. What she doesn't tell you, though, is this: She wasn't being safe all along. She wanted to have that baby— and the way she saw it, this was the only way to make it happen.

Here's how a scenario like that played out in real life. Jody (not her real name), a 32-year-old account manager for a major New York ad firm, decided to speed things along with her boyfriend two years ago by getting pregnant without telling him. "It's not about trapping the guy," Jody says. "That's kind of old-fashioned. Yeah, you want him to be into it, but there are other ways to get a guy to commit. If you're smart and in a good relationship, it's just about the fact that you want a kid." Even in her circle of young, urban, and gainfully employed friends, Jody says, this particular brand of subterfuge isn't exactly condemned the way one might expect. In fact, it's sort of, well, normal. "I see and hear people talk about it, and I understand. I get it," she says, "and I don't even think it's that manipulative. It's more like, 'Hey, the timing is right for me. I got pregnant—oops! Well, it's here, let's have it.' I think that's more the way it is now than it was back in the day when you had to marry someone before you got pregnant. Marriage doesn't matter now."

Railroading a guy into parenthood isn't just some "baby daddy" soap-opera scenario. You'll never hear the ladies'-room chatter that leads people like Jody to feel justified, but to get some idea of it, consider this: A woman's fertility peaks when she's between the ages of 20 and 24, according to Mayo Clinic statistics. By the time she's 35 to 39, it's already wilted by 25 to 50 percent. And from there the options aren't always so attractive: The average cost of in vitro fertilization in the United States is $100,000 per baby—and insurance generally won't pay a cent. Combine that with the shifting social mores about single motherhood and having kids outside of marriage, and you've got a pretty good explanation for why some women, particularly ones in stable relationships, don't see this as trickery at all—it's more like a nudge.