After a woman hits the age of 25, her ovaries shrivel up like walnuts, detach from her falopian tubes, and start a slow descent to the floor along with her self-esteem and happiness. That is - we hope - obviously not true. But it is not far from how some women are made to feel by the pressure to procreate early in life.

Part of that strain comes from figures so bleak they are enough to make even the most happily childless among us pause for thought, if just for a second. One such oft-cited statistic is that one in three women over the age of 35 will not conceive after a year of trying. This is not helped by the pervasive scaremongering.

The first known reference in the media to a woman's 'biological clock' was a column in The Washington Post in 1978 headlined it is "ticking for the career woman". Countless other articles have followed since. This sentiment was mirrored more recently in a 2015 Daily Mail piece quoting a consultant gynaecologist who said that women risk experiencing "shock and agony" if they wait until 30 to try for a baby.

The fear appears to stem from a confusion surrounding statistics muddied by the sense that bearing children is a woman's sole purpose. It also suggests that women who are reliant on IVF treatment are a drain on public funds. After all, a man's fertility also drops past a certain age but that is hardly debated to the same extent.

Few are more aware of this than Jean Twenge, a psychologist at San Diego State University who decided to try for her first child with her new husband at the age of 34.

She was unnerved to discover that conception had gone from certainty to the equivalent of throwing the fertility dice at her relatively young age. As an academic, Twenge was not prepared to simply accept those odds. So she set about finding where the statistics originated from.

Twenge was amazed to discover the figures were based on a French study of women from 1670 to 1830 in France, 30% of whom were found to be childless, orchestrated by a 2004 article published in the journal Human Reproduction. The birth records do have some merit as it is hard to draw conclusions from data on modern populations where birth control is used, but of course are hindered by the fact that they refer to a time before the advent of modern medicine, including contraception and the choice that comes with it. These findings are outlined in her book, The Impatient Woman's Guide to Getting Pregnant.

"When I found out that the 'one out of three' statistic was based on French birth records from the 1700s, I laughed," Twenge tells IBTimes UK. "I had already read the more modern research suggesting that fertility in a woman's late 30s was considerably better than that, so it finally explained the discrepancy. Now it made sense why the numbers in the research and what was on websites and books was so different - most of the websites and books were using this study of women from hundreds of years ago." It seemed that the more shocking data simply fitted into a damaging narrative about womanhood and childbirth.

"When I found out that the 'one out of three' statistic was based on French birth records from the 1700s, I laughed

Women can breathe a sigh of relief that a widely reported 2004 study found that those having sex twice a week will see their chances of conceiving within a year drop just four percent from 86% aged 27 between 34 to 82% for 35 to 39-year-olds. Rather than the 17th century subjects, that study involved around 780 women across seven European countries. A separate research carried out by Danish scientists in 2013 showed that 84% of women aged between 20 and 34 got pregnant within a year. That figure dropped to 78% for those aged between 35 and 40.

Fertility does of course deplete as women, and men, grow older. And the risk of chromosomal abnormalities, which can cause conditions such as Down's syndrome, increase slightly from one in 500 aged 20; one in 400 at 30; and 60 to 70 at 40. The majority of women, therefore, will not be affected. Further complications lie in the effectiveness of IVF and artificial insemination, changing between the early 30s and late 30s, David James, of the UK's National Institute for Health and Care Excellence, told BBC News in an interview. A large increase in abnormal embryos does not occur until after age 40, adds Twenge. The question lies in whether it is worthwhile for a woman to rush into having a child at the wrong time with the wrong person to avoid the slightest chance she will have a child with disabilities or need further fertility treatment.

Asked if the pressure on women to have children as early as possible is justified, Professor Simon Fishel, the founder and president of the Care Fertility Group set to speak at London's Fertility Show in November, tells IBTimes UK: "It is warranted if pure biology were the driving force." Which, of course, is not the case. If it were so we would be living in a real-life version of The Handmaid's Tale.

"The efficiency of successful conception is without any doubt the age of the woman's eggs - so a woman in her 50s using eggs from a 30 year-old, for example, would have the chance of a successful conception close to the incidence of a 30-year-old," Professor Fishel explains.

"So, yes, biologically it is very sensible to have children earlier – just for very many women social pressures and modern way of life make this a pipe dream. It's a role of the evolutionary dice, affecting mainly genetics when it is age-related," he adds. "General fertility issues are another story and there is also a significant effect of lifestyle and or environment."

Gemma McCrae is proof that women can have healthy children even if they are skirting 40. And the 41-year-old life coach from Berkshire is far from alone. In 2015, the fertility rate of women aged 40 overtook that of women aged below 20 for the first time since 1947, according to the Office for National Statistics.

Gemma McCrae
Gemma McCrae is pregnant with her second child at the age of 41

McCrae was aged 39 when she first tried to conceive with her husband. She was deluged with "too many comments to recount" about what was apparently taking her so long.

"I think I'm very typical of professional ladies today," she tells IBTimes UK. "My career took centre stage and yes I had relationships, but I didn't want to get married until I met the right one. He didn't come along until I was 35. We got married when I was 37 and we waited to try for children because I didn't feel ready. I wanted time just with my husband because I realised once kids come along how life changes."

Unusually, perhaps, McCrae was not concerned about her chances of conceiving. The anecdotal evidence that women had been "having kids well into their 40s for years" was all around her. Her sister had her niece at 39, and another member of her family had become a mother twice at the age of 46 - and that was in the 1950s.

McCrae struggled more with the misconceptions about expecting at a later age than conceiving.

"I didn't struggle," she says. "I got pregnant as soon as we started to try but unfortunately it ended in miscarriage." Without studying the bi-product of the miscarriage, it is unclear whether it was her age which caused it, particularly when one in four women will experience one.

"I've been gobsmacked by the prejudice I've received, particularly during my previous two miscarriages," she says.

I've been gobsmacked by the prejudice I've received

Blood tests proved that although she did not have the fertility of a 25-year-old, her levels were normal for her age and there was no reason for her not to become pregnant.

"However, the fertility team I encountered running up to meeting with the consultant came out with ridiculous comments. In one of my first appointments I was clearly told I was unlikely to conceive a healthy baby because of my age and should consider egg donors. This was before all my bloods had come back and they knew what they were dealing with," she claims.

"Also, after my second miscarriage, the doctor bluntly told me I had miscarriage because I was older. Those were her exact words. If I wasn't so strong of mind and researched fertility, I strongly believe I would have had egg donor or adopted by now.

"Lastly, in terms of chances of conception, I was clearly told IVF would only have a 10% chance of working. However, as we all know, it takes one good egg to be fertilised so I didn't listen to anyone and we carried on trying."

Now almost 41, McCrae is expecting her second child.

"Do not feel pressurised by the system," stresses McCrae. "You can have kids later on in life, it's been happening for hundreds of years. However, it may be worth considering having your eggs frozen in early or mid thirties as a precaution just in case.

"We must be realistic, getting pregnant later on in life will probably take longer. But it doesn't mean you can't. Until the menopause hits, a woman can have kids. That's a biological fact."

The conclusion is clear: statistics of course have their uses, but with differences between individuals so varied, the importance of being ready to have children should always trump fear.