Back in 1973, my mother had a baby. I was 11 at the time and remember her pregnancy well. It was planned, but for my mum it felt very last-ditch. "I'm too old for this," I remember her saying, as she packed her hospital bag.
She was 35 – by today's standards a spring chicken. Figures released last week show that more and more new mothers are now aged 40-plus: the number of births in this age group has trebled in the past 20 years and is still on the rise. In 1989 there were 9,336 births to fortysomething women, the government statistics for England and Wales show; by 1999 the figure was up to 14,252; and last year, it was even higher, at 26,976.
I've been in tune with the statistics in my own obstetric career: while my mother had her first baby – me – at 24, I had my first baby at 29; while she had her last at 35, I had my last at 39.
So what will things be like for my own four daughters? On present trends, I shouldn't expect to become a granny until my eldest daughter is at least in her mid-thirties, and some of my daughters will probably be pushing babies out when they're the age I am now – 47.
But of course things can't go on like this, as well-meaning obstetricians keep warning us: our social, financial and career expectations may favour childbirth late in life, but alas for us, our physiology pulls us in an entirely different direction. Women's bodies are best at conceiving, at nurturing and at birthing babies when we are aged between 20 and 30 years of age. It might not sound palatable, but it's a fact: that's when we're designed to do it, and that's when we do it best. And the consequences of ignoring this can be tragic: most of the women who find it difficult or impossible to conceive or bear a child in their late thirties or forties would have had no trouble 15 or even 10 years earlier.
So what do the next generation of mothers think? Rosie, my eldest daughter, is 18 and hoping to go to university in October. Like most smart, ambitious young people she's keen both to find the career that's right for her and to enjoy her work. But she's also keen to have children. And, she says, she's not waiting as long as I waited: she'd like to have a child by her mid-twenties. Nor is she alone. Many of her friends, some of them only children born to mothers already late in their thirties, she says, are thinking along similar lines.
So will our daughters buck the trend, and would they be right to do so? Of course it will be tough for them, because reversing trends is always difficult for those in the vanguard of change. The world of work is geared to early-career acceleration, so taking time out to have babies young can seem like a bad move. But would it really be so misguided?
My instinct is that my daughter and her friends are right: at their age, every hormone in their body is screaming at them to reproduce. It's all very well to suppress that drive, and to go on suppressing it throughout your twenties – but who's the winner, and who's the loser?
A career pattern that builds quickly in early life and levels off in mid-life has become very much the norm in western societies. But it's a pattern that favours men a lot more than it favours women. Not only does it steal our best childbearing years; it also puts us out to grass just when we should be claiming our biggest workplace success.
Here's why. A woman's hormones, in her childbearing years, are heavily weighted towards her nurturing and caring qualities: all that oestrogen coursing through the body of a woman in her twenties and early thirties programmes her to feel drawn towards looking after others, and towards putting other people before herself.
Not all women feel this way, of course: but in broad terms, and compared with testosterone-charged men, this is how we feel and behave. We're less ruthless, less cut-throat, more caring. We turn it to our advantage, ideally, but it can make life tricky for us, especially in a male-dominated workplace.
Fast forward 25 years to the age I am now and everything changes. In our forties, as we near the end of our childbearing years, our hormonal make-up alters dramatically. Oestrogen levels plummet: that puts the "male" hormone, testosterone, in the driving seat. So for the first time since puberty, women are on a similar hormonal footing to men. Instead of focusing on their own needs, they are now geared to pay attention to their own situation, to their own goals and their own opportunities. What's more, they've got more ruthlessness, more drive and more ambition.
What's happening to men at this time? Well, interestingly their testosterone levels are actually falling – and testosterone has been linked, in studies, with financial risk-taking and career success in men. So at precisely the moment when men are ready to take their foot off the gas and slow down in their career, women are getting ready to rev up.
So there are no prizes for guessing why professional life ebbs and flows in the way that it does: it all makes perfect sense, providing you are male. But things could be different, and into the bargain we could get motherhood at a time that suits us better.
Suppose, just suppose, that a young woman like Rosie finds the man she wants to raise children with by her mid-twenties. She's got a degree by then, and maybe a postgraduate qualification: and she puts these on ice to have her babies. Eight years later, when her children are at school, she goes back into the workplace to start her career properly. Her workload builds, but not too quickly, because she still has parenting responsibilities, as does her partner. But as the years go by, her children need her less and she is able to achieve more.
By her mid-forties, she's at full throttle and her physiological make-up is working entirely to her advantage. She's more ruthless, more determined, more hard-nosed than she's ever been, and she has the time, the space and the drive to put these attributes to use and to get what she wants from the peak years of her career.
If Rosie does find herself in this position in 30 years' time, she'll be a lot luckier than many of my contemporaries. Many of the women I see around me today struggled through increasingly burdening careers in their thirties before accepting redundancy or a career break gratefully in their late thirties when a baby finally appeared. For a while they were happy to be out of the workplace, raising that child and perhaps another one or two . But now, in their late forties, their children are less needy and my friends are bored and unfulfilled. They feel they've got the energy and the enthusiasm to be taking on a challenge, but that challenge is nowhere to be seen.
In career terms, they're past it, just as in childbearing terms they were past it when they decided to try to conceive.
Could it be different? Sure it could, but we have to rewrite the rule book. It won't be easy, but there's a lot at stake. Early career/late babies spells – as is increasingly becoming obvious – problems and unhappiness for many women. Early babies/late career could, whisper it where you will, spread happiness and success.
Maybe Rosie and her friends really will turn the world around. And perhaps, just perhaps, they will manage to be the generation that really does have it all.