The number of women having babies in their forties has doubled in the past decade. I'm reluctant even to write about it, because it is precisely this kind of media coverage that encourages younger women to think, insanely in my view, that delaying motherhood until you’re middle-aged is a reasonable and straightforward thing to do.

They flick through magazines and look at pictures of Madonna, whose second child was born when she was 41, or Emma Thompson, whose daughter was conceived by IVF when she was 40, and conclude that anyone can put motherhood on ice until they’re “ready” – until their house/car/job is impressive enough, until they’ve met The One, until they’re mentally prepared for having a child.

On paper, this approach looks as though it might have some merit. But real life isn’t paper. We all know enough biology to know that the best time to have a child, as in the time when you are most likely to conceive with no complications and have a healthy baby, is when you are young, which means late teens or early twenties. We also all know that women’s fertility declines sharply, and then goes into freefall, past the age of 35.

These are facts. And it’s facts we should be sticking to, rather than semi-delusional fantasies based on what we read in trashy magazines about some super-rich middle-aged celeb who can afford the kind of exorbitant fertility treatment that would finish most of us off, both emotionally and financially, because you don’t get IVF on the National Health Service if you’re 20 years away from being pensionable.

I am put out by the way childless women of my age (41) have started talking breezily about IVF as though it were a procedure not dissimilar to Botox. IVF involves artificially inducing the menopause and then reversing it. It’s hardcore. You don’t just go and have it done in your lunch hour and then forget about it, and from what I observe it puts incredible stress on relationships (and sex lives).

Yet I meet otherwise intelligent women who talk about it as though it were simply a matter of signing up to the programme and bingo, a baby. Aside from anything else, IVF doesn’t meet with much success with the middle-aged; ordinary mortals are more likely to be turned down for treatment on grounds of age than provided with instant triplets.

I really love babies and I’d love to have another three, but the simple fact is that I’ve left it too late. When it comes to pregnancy and fertility, women of my generation have been fed a complete lie by the feminist movement, which is that you really can have it all – a career, success, money, status – and, when you’re done with those, when you've reached the top of your particular greasy pole, as many children as you like – no hurry at all.

The truth is there is a hurry and, like it or not, biology does discriminate. Sure we can try to do something about it and put ourselves through traumatic medical procedures to try to claw back a scrap or two of youth, a nice plump load of eggs to replace our withered ones, but I’m tired of hearing this spoken of as if it were both the norm and perfectly natural. It isn’t.

Lots of women get pregnant naturally in their forties and good luck to them; I’m not saying no one should have a child past the age of 35. Nor am I opposed to IVF (although I do have questions about what the long-term impact is on women’s health).

What I do oppose is the line that being an older mother is a really marvellous ambition and easily achievable. I know lots of older first-time mothers and they’re absolutely knackered. They stagger around, broken with lack of sleep – because getting up three times in the night when you’re 43 is not the same as doing it when you’re 25 – with huge rings under their eyes and husbands who notice the latter and wonder what happened to the minx they married.

These women are madly in love with their babies of course, and that’s lovely, but they are bewildered by everything else, as you would be if you’d had an extra 20 years of “me time” and were suddenly asked to become the acme of selflessness. If they’re on maternity leave, they find hanging out with the teenage mothers at the One O’Clock Club faintly disheartening, to say nothing of mind-bendingly boring. They’re the oldest person there by miles. One of my friends is older than another child’s granny, who is a mere 39.

Making “mummy friends” is bad enough when you’re young – it’s why most people go to NCT classes – but at least some of your contemporaries are likely to be pregnant too. That doesn’t happen if you’re pregnant for the first time at 42: your friends with older children have their own preoccupations, your childless friends resent you and you’re left on your own, pushing your buggy around the park in the rain and having to force yourself to make new friends in order not to die of loneliness. You may be more patient than the younger mums, but you’ll need to be.

What amazes me most of all, though, is the sweetly retro notion of mooching around pining for Mr Right, as the clock ticks away and you want a baby so badly that you start eyeing newborns up in supermarkets and finding yourself filled with a strange sense of rage when your pregnant girlfriends discuss breastfeeding. My advice to all my girlfriends, and to you, should this ring a bell is: just do it. Get pregnant. Don’t wait. Mr Right can turn into Mr Wrong overnight: there are no certainties.

Besides, if he’s really Mr Right and he comes along a few years down the line, he’ll love your children because he loves you and you love them. Careers can wait: nothing terrible is going to happen if you take a couple of years off. As for houses – and this is another one I hear all the time: “We don’t have the room” – a baby is a very small creature. My first one lived in a basket in the kitchen for months, happy as a clam. The idea that the optimum condition for motherhood involves a five-storey house is nonsense.

Another story last week showed that women who have the foresight to freeze their eggs are leaving it too late, too. A fertility expert from the University of Aberdeen said: “Increasing numbers of women are coming to us in their thirties and forties for IVF whose outcomes are poor. Egg freezing has to be carried out when women are much younger; if you’re in your late thirties it defeats the whole purpose.”

Harsh, but true. If you really want a baby, there’s no time like the present.

india.knight@sunday-times.co.uk

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