As entertaining as this may be, it is of course important to always remember that getting pregnant in your mid 40s is much more difficult than in your mid 30s. In terms of reproduction, there is no time to lose – attempts to improve outcomes with older eggs have generally been very disappointing so far.

– Dr Gavin Sacks

Like all great comic creations, Bridget Jones is timeless, though she is not ageless.

In the new film, Bridget Jones’s Baby, Helen Fielding’s 43-year-old heroine is no longer knocking back the Chardonnay or counting calories, although she does face some weight-gain issues in the shape of a puzzling pregnancy bump. But who is the daddy, darling? Bridget can’t decide.

Along with millions of other women, I will be racing to my local cinema with a tin of slimline G&T, a straw and several similarly equipped girlfriends. We can rely on Bridget to make us laugh like drains. Who cares whether that perpetual adolescent is capable of graduating to the self-free combat zone of motherhood? It’s only fiction, isn’t it?

Well, yes and no. Bridget Jones was real enough to a generation of neurotic singletons. She deplored Smug Marrieds while exuding a bewildered sense of loss as a woman’s traditional role was altered beyond recognition. She had a career, but she wasn’t much good at it. Her heart was in romance.

In any previous generation, Bridget would have been a nice county gel settling down with a Rufus, an Aga and three daughters with names ending in “a”, not living in fear that she would die alone with cats.

We all cheered when she finally bagged her own Mr Darcy. Little did Jane Austen suspect that, 200 years later, her maxim would be adapted to read, “It is a truth universally acknowledged, that a single woman in possession of big pants must be in want of a husband, but she will be too ashamed to say so and he will be too fickle to commit.”

Bridget Jones undoubtedly has a huge influence beyond the covers of a paperback. The problem I have with the new movie is that adorable Bridget becomes party to the big Fertility Lie.

Put it this way, how many 43-year-olds do you know who fall accidentally pregnant? All the fortysomething women I know who don’t have children are trapped inside what one gynaecologist calls “the brutal cycle of IVF, adoption and regret”.

If you haven’t had a baby by the time you’re 43, the chances of you getting up the duff from a one-night stand are about the same as you finding a childless fortysomething male who isn’t a practising homosexual or a priest.

Young women are told today that “40 is the new 30”. Unfortunately, their bodies didn’t get the memo. Alex Jones, presenter of The One Show, is not stupid, far from it. But the 39-year-old admitted earlier this year that it hadn’t really occurred to her she might have trouble starting a family until she got married last December. Yet her fertility window was closing fast. As Alex said, girls spend so much of their youth practising safe sex that you forget you need to start the unsafe kind in plenty of time to have kids.

“This is a dangerous trend, and women quite often have unrealistic expectations about fertility,” according to Mark Perloe, an American specialist in reproductive endocrinology. According to Dr Perloe, at the age of 43 Bridget Jones is more likely to have a miscarriage than a baby.

A study published in the British Medical Journal, of more than 600,000 women in Denmark who had a pregnancy between 1978 and 1992, bears out that bleak prognosis. It showed a steady, age-related rise in rates of miscarriage – from 9 per cent among women in their early to mid-20s to a staggering 75 per cent among women aged 45 and older. The increase was already considerable among those in their 30s.

Yet, the trend is for women to ignore science and start their families later and later. According to recent figures, women over 40 are now having more babies than women under 20. This is almost entirely due to career pressures and house prices. Older motherhood has its advantages, sure, but the dangers are too often ignored.

Look at Nicola Sturgeon. Scotland’s First Minister just made public her own miscarriage at the age of 40. The SNP leader said that she hoped that the revelation would help to break a “taboo”. She wants to challenge “assumptions and judgments” made about political leaders who do not have children. Ms Sturgeon was upset by a New Statesman cover showing her and other childless female political leaders, including Theresa May and Angela Merkel, standing round a cradle that contained only a ballot box.

Look, any woman who has gone through the trauma of miscarriage has my deepest sympathy. I will remember my own till my dying day. The baby that nearly was can be every bit as real as the ones that are. But I can’t help feeling that Nicola Sturgeon is being slightly disingenuous.

Did she get pregnant so late in the day because a political career made any other option difficult? No one would judge her for that, but there is still far too little openness about why so many of our most powerful women don’t have kids.

The fact is women are only truly on a level career playing field with men when they are not held back by parental responsibilities. Women still do the lioness’s share of childcare and housework, and only the lucky (or wealthy) few can afford to pay a nanny, or are blessed with a househusband. This painful, intractable inequality is the real taboo that needs to be broken.

Why can’t we just be honest and say that most mothers would be hard-pushed to have the single-minded focus on politics that makes a Sturgeon or a Theresa May? I feel glad that two such capable women are holding the reins of power and, if not giving birth helped them to get there, so be it.

Let’s also be frank about the vast resources and backstage support team a successful woman needs to pass for a man. We are only going to change that on the day someone asks a young guy: “So, Josh, how are you planning on combining a career with fatherhood?”

Until then, women will continue to postpone having a family to fit round a workplace designed by men for the convenience of men, and too many will suffer the misery of miscarriage and infertility.

Alex Jones has just announced that she is pregnant. Like her namesake, Bridget, the BBC presenter is one of the lucky ones who got pregnant late. Alex believes young women need to be taught about fertility every bit as much as about contraception. I couldn’t agree more.

Girls, please don’t trust Bridget Jones. She’s a hoot – but a baby at 43 is pure fiction.

Article originally published on the on September 6 2016. Written by ALLISON PEARSON