10/08/2013 10:50 am ET Updated Jan 23, 2014

Not Often and Early, But Rarely and Late

I recently took part in an all-female panel discussion about women's changing lives, along with some of London's leading female newspaper columnists and major feminist campaigners.

Everyone but me strongly recommended having children later rather than sooner. That way, they argued, one's career was well established in advance of any break. I thought it was better to do the opposite, if possible: have children young and then have a clear sweep through middle age, guilt-free and relatively unexhausted. But I was not only outvoted on that particular panel; I am out of step with the temper of the times.

Having babies later and later is what occupationally successful women do. As we have already seen, large and growing numbers -- unlike unqualified high-school dropouts -- have no children at all. But highly educated women who do have children are also diverging from other women in when they have a child. They are having their children later and later, not only in absolute terms, but compared to everyone else.

As recently as the late 1970s, not even 40 years ago, having a first child after the age of 30, let alone 35, was highly unusual for women of any class. It had been equally unlikely throughout the previous centuries. The idea that it would be "normal" to have one's first child after the age of 30 would have seemed completely extraordinary to any past generation.

That has changed totally. Turn up at the hospital as a pregnant 35-year-old in labor and you'll be met with something of a yawn: this is routine stuff. Turn up as a 35-year-old first-time mother and the yawn is only slightly smaller. Not only late childbirth, but late first childbirth is now standard. Among American female graduates, the years between age 30 and 35 had become, by 2006, the peak child-bearing period. It is the same in the UK, where the proportion of graduates having a baby before they are 30 halved in the last few decades; the same in France. The pattern is international.

Live among today's graduate and upper middle classes and you might get the impression that no one even contemplates pregnancy until 30 looms. In fact, you couldn't be more wrong. Most female high school dropouts complete their families well before they reach their mid-thirties. In the U.S., four in five female dropouts are mothers by the age of 25, while in Britain, about half of all native-born women without qualifications become mothers by the time they are 22. And other, more educated but non-graduate women also have their children at what used to be a "normal" age; for those with some college or a two-year degree, the peak is between 25 and 39.

Only for mothers with full bachelor's degrees, or more, does 30 signal the start of peak child-bearing years. And only for them has there been a major change in the likelihood of having a first child after the age of 30.

It is clear how and why so many graduate women (and men) end up with few children or none. It is from a whole succession of more or less conscious choices about career and relationships, and the relative attraction and cost of one path over another. But there's one other factor too. Sometimes, it is the unintended consequence of delay.

Few of us, as we have seen, always intend to be childless. And few of us say that we want an only child, or think that is a good idea in principle. But the older you are, the dicier conception becomes. Past 35, women's fertility drops fast. Modern medicine seems to offer miracles, the chance to ignore and bypass biology. But at 40, fertility is way down, far more than most people realize.

Professor Peter Braude of King's College London is one of the world's foremost academic experts on fertility and assisted reproduction. I asked him about fertility as one gets older, and in particular about the chances of getting pregnant via IVF (in vitro fertilization).

If you say what would be the likelihood that I would get pregnant at the age of 35, probably about one in three will go home with a live birth. If you say what is it likely to be when I'm age 40, probably about one in 10 will go home with a live birth. And if I'm 42, probably now we're going down to about one in 20...

We do a presentation in our own clinic for all our patients who come along every month and we show them the real figures saying that the likelihood of going home [pregnant] is so much. When patients come and they've not got pregnant, and they come back to see us, the first question I ask one of them is, 'What did you think the likelihood of going home with a baby was?' They'll say, 'Not very good.' So I'll say, 'Well, what do you mean?' 'Oh, about 80 percent.' And then I ask the other one, 'What do you think?' 'Oh, 50-50.' And I say, 'Where did you get that number from? We never told you that.' That is the wish; that is the presumption of what they're really hoping to happen. There's plenty out there in the literature, but people don't want to hear that, they really don't.

Part of this, Braude explains, is because of the "lucky fertile," who have babies at 39 or 40, can't see what the fuss is about and say so to everyone they know. But it is also the media coverage.

You suddenly see some film star -- 47 -- has twins and you probably think, ooh isn't that marvelous. [But] that woman had the twins because she had ovum donation using eggs from a younger woman, because she couldn't get pregnant herself.

People come to us having had significant careers, having made a lot of money, having achieved what they really want to do, and say, OK, now's the time I'm going to have my family. And they can't pay for it, they can't buy it, they can't work hard for it and it just doesn't come.

It's very hard when you're younger to think about the future. I mean, how many of us really are thinking about our pensions and our life insurance when we're 21 years old? We don't. And it's exactly the same sort of thing. When you have a good job and you're running a bank or you're looking toward running a bank, or whatever it is, you'll say, well, I'll get there when I'm 35. Then I can have my family.

It's really very difficult for women. They're at their fittest, they're at their brightest, they're making things happen and they feel they've got to keep along that track. And there is nothing that easily allows them to take a break.

Predicting the future is a game for deluded optimists; but are elite women, en masse, going to downsize their careers anytime soon? It seems implausible. In which case this century's story will be one of male and female elites who are alike in this respect too: they will have fewer children than their contemporaries, and many will have no children at all.

Excerpted from The XX Factor: How the Rise of Working Women Has Created a Far Less Equal World by Alison Wolf. Copyright © 2013 by Alison Wolf. Published by Crown Publishers, an imprint of the Crown Publishing Group, a division of Random House LLC, a Penguin Random House Company.