Women who want to have kids should make it a high priority in their early twenties to find a partner. A Newsweek cover story, Marriage by the Numbers, says is okay to wait until after 35 to get married. Newsweek is revising the saying that a woman has more chance of getting hit by a truck than getting married after age 35.

But the article ignores one of the most pressing issues facing Generation X: Infertility. No generation of women has had more trouble with fertility than this generation who received the terrible advice, “Wait. You have time. Focus on your career first.”

In fact, you have your whole life to get a career. This is not true about having a baby.

Even if you are past your early twenties, or not heterosexual, if you’re single and want to have kids with a partner, you need to find one now. Take that career drive and direct it toward mating because your career skills will outlast your ovaries.

In case you think you’re waiting for “the right time,” there is no evidence to show when in a woman’s career is best to have kids. At any point, she is thrown off track. At any point when a woman has kids, statistically she will start to earn less money even if she takes no maternity leave whatsoever. There is no evidence to show that it’s easier to take time out of the workforce at a certain point in a career. People just plain don’t know.

Phyllis Moen, professor of sociology at the University of Minnesota, told me in an interview, “Don’t wait until the right time in your career to have a child or it will never come.”

However there is lots of evidence to show that a woman’s biological clock takes a nose-dive at age 35. I know, because that’s when I started having kids. The geneticist showed me and my husband a graph of Down’s Syndrome and we nearly keeled over when we saw the cliff at 35. We had no idea. That Down’s Syndrome cliff, though, is a stand-in for everything, because a huge percentage of fertility statistics get bad at 35.

There is also lots of evidence to say that having kids at least two years apart is best for the kids. However there is a distinct advantage for first-born kids. They are richer, smarter, and as if that’s not enough, year after year 90% of Harvard’s incoming freshmen are first-born. You can mitigate the impact of birth order on your second child by having three years between kids.

If you start when you are thirty-one, you can have two kids, three years apart, before you’re thirty-five. But this plan does not take into consideration that about 20% of pregnancies end in a miscarriage. This means you have almost a 50% chance of having to go through three pregnancies to have two kids, which means you should start when you’re thirty.

If you want to have babies when you’re thirty, then you probably want to be married when you’re twenty-eight. This is good news because if you marry very young you’re more likely to get divorced, but the statistics get much better if you wait until you’re twenty-five. For a healthy marriage, experts think people should be married two or three years before they consider having children. A reasonable expectation is to meet someone, date for a couple of years, and get engaged with almost a year’s time to pull off a wedding. So you need to meet the person at age twenty-four.

So this means that it may make sense for men to work full-speed ahead on their career in their early twenties, but women cannot afford that. Women need to make time in their lives to search for a mate in the same systematic, focused way that women have been searching for careers in their early twenties. And don’t tell yourself you’re waiting until you know yourself better. Getting to know yourself is a lifelong process, and after age twenty-five, waiting to get married won’t decrease your chance of divorce.

The good news here is that a large body of research shows that you will gain more happiness by being married than by having a good job. Yes, you should not have to choose between a good job and marriage. But this column is not about what is fair or what is just. It is about what is real.

You have a biological clock that does not pay attention to issues of social justice. You cannot control your biological clock and you cannot control the workplace. But you can control where you spend your time and energy, and you should look hard for a husband early on. Line up the marriage first, then the career.