All too frequently, I am faced with breaking bad news to disappointed couples in their early 40s who expected IVF to solve their fertility problems. The sad truth is that there's often little I can offer if the woman is much over 40, apart from egg donation from a younger sibling, friend or donor.

Many of these couples have read about the recent scientific advances that have led to significant improvements in assisted reproductive technology. But what's not so well understood is that these advances really apply only to women in their 20s and 30s. Today, just 12 per cent of IVF cycles in women over 40 result in the birth of a baby.

The poor quality of eggs in "older" women is now the single-biggest challenge facing fertility specialists around the world. It's a crucial message that still does not always get through to Generation Y as they enter their important child-bearing years.

Men and women are tending to delay the traditional markers of adulthood. Marriage and children have given way to travel, career aspirations and a mortgage, just at the time fertility specialists like me would be advising them to think seriously about starting a family. 

There is already technology available to women in their early 30s to help them predict their future fertility. The AMH blood test, available from a GP for about $80, is a good indication of how many eggs women have. I'd recommend all women who plan to start a family and who have not yet done so by their early 30s to take this test as a measure of how many "good" reproductive years they have.

Women between 30 and 37 who are not yet ready to start their family might also consider "egg freezing", where we harvest eggs and snap-freeze them in liquid nitrogen. This process is yielding impressive results but again the chances of success are reduced when the eggs are extracted after the age of 35.

We are also on the cusp of exciting discoveries in the laboratory, which are explaining what goes wrong with women's eggs as they age, meaning we may one day be able to prolong the fertility of older women. Such treatments are a way off as yet but understanding the basic science of ovarian ageing should lead to safe ways to delay loss of fertility and also delay menopause.

From a societal point of view, what worries me is what demographer and social commentator Mark McCrindle refers to as the "safety net syndrome" – the perception held that someone, whether it's the government or medical science, will solve the problems that have arisen because of a person's own choices. When it comes to fertility, that's simply not possible.

There are, however, promising signs that the pendulum is starting to swing back. McCrindle's research indicates that Generation Z is rejecting the "have it all" attitude of the previous generation and is recognising the limitations of science when it comes to fertility.

The other challenges are ethical. Medicare funding for assisted reproductive technology is not currently age capped, but one wonders how long the public purse will continue to subsidise this aspect of care. Medicare will provide support only for treatment of infertility, so "social" egg freezing can be costly. The emotional costs to women are also highly significant. Most fertility specialists are honest in telling couples the truth about their chances of success, yet we still hear of people continuing to undergo multiple cycles of IVF despite almost no hope of having a healthy child.

It is important that ethical guidelines keep pace with the speed of scientific discovery. I am a member of the National Health and Medical Research Council committee that is rewriting ethical guidelines for assisted reproductive technology in Australia. The guidelines will cover, among other things, sex selection of embryos, regulations around surrogacy and whether women should be paid for donating eggs. Public consultation on these questions is about to start and it's a conversation we need to have.

It's not fair to expect the responsibility for the reproduction of the species to rest solely on the shoulders of young women. How we prolong fertility into later adulthood is a question we all – scientists, governments and the community – should carefully consider.

Professor William Ledger is head of UNSW Medicine's School of Women's and Children's Health and professor of obstetrics and gynaecology. He will deliver the UNSW Medicine Dean's Lecture "The Ticking Clock: Demographic Change and Future Families "with social researcher Mark McCrindle at UNSW on Monday night.