Some people hear and respond to their biological clock when it is just an annoying tick in the background while others, happy to ignore it, find by the time their fertility alarm bells sound they have to place hope in medical technology to fulfil dreams of parenthood.
Too often by the time family plans make it to the top of the modern "to-do" list, reproductive capacity has plunged to the point where the odds are stacked against easy success, say reproductive medicine specialists.
And while increasingly sophisticated technology now allows doctors to better assess fertility and assist the conception process, it is still not able to cheat ageing biology, with success rates remaining low as mothers enter their 40s.
Lincoln Brett, head of obstetrics and gynaecology at the Notre Dame University school of medicine, says women are still not getting the message about the nosedive in fertility that happens after the age of 37 or, even if they know this, may be restricted by social factors such as not having a suitable partner.
"There are the ones who don't have a bloke and others have put it off because they have other things to do and then we find it is too late," says Associate Professor Brett, who also consults at Hollywood Fertility Centre.
"Fertility should not take a back seat to the PhD or corporate ladder.
"There wouldn't be a week go by where a woman wouldn't drop in to see me to say she would like to have a baby but she is well into her 40s and there is no chance I can help get her pregnant so I have to turn her away.
"People haven't got the message."
Professor Brett says "take-home baby" IVF success rates for 40- year-olds is about 5 per cent, dropping to 3 per cent by 42.
In 25 years of operation, he says, Sydney IVF, which operates clinics around Australia including Hollywood Fertility Centre in WA, had only ever achieved one pregnancy in a woman over 45.
Ambitions to freeze eggs by women who know their reproductive years are nearing an end also usually result in disappointment because, unlike the freezing of fertilised eggs (embryos), the procedure remains largely experimental and prohibitively expensive, he says.
"A month wouldn't go by where I don't have a woman coming who says 'I'm 35, single and hoping to find a bloke but haven't at the moment so can you freeze my eggs," he says.
"Of all the Sydney IVF clinics, we have had one pregnancy in Australia from frozen eggs and it cost $10,000 to do."
He says early menopause, which can even occur in women in their 30s, also trips up the family plans of some couples.
Reproductive biologist Bruce Bellinge, managing director of Concept Fertility Centre, says IVF has not improved the chances of older women getting pregnant unless they use donated eggs from younger women.
"It is the age of the eggs that is more of a problem than the age of the woman," Dr Bellinge says.
"An older woman can get pregnant quite happily if she uses younger eggs or embryos from a younger woman. The utero environment doesn't seem to be affected at all by age."
But with the chance of conceiving naturally in the mid-40s as low as one to two per cent, he advises couples to start families earlier.
"There is always an expectation that we are fertile and we spend most of our youth suppressing our fertility," Dr Bellinge says.
"Then when we lift that suppression, we expect to get pregnant and if it doesn't happen, it is a real shock to the system.
"I don't think people really consider fertility as anything except their birthright."
Concept Fertility Centre clinical psychologist Iolanda Rodino says she is being called on to counsel an increasing number of older women who have left trying for a baby until later in life.
For many the shock of their decreased chances was the first real life hurdle they had faced.
"We are seeing women who say they feel like they are 30 and they even look like they are 30 and they have well-kept bodies that are functioning well," Ms Rodino says.
"But they still have the ovaries of a 40-year-old."
Being reminded of this often does not fit well with their self-image and can be a challenge to their self-esteem, she says.