As every unattached woman in her twenties or thirties out there is well aware, the most important factor determining her chance of achieving pregnancy is age.
In broad terms, fertility starts to decline when women are in their early 30s, the rate of decline speeds up at around age 35 and by age 40 and beyond, the chance of pregnancy is slim and the risk of miscarriage high. This is because, as women age, the quantity and quality of their eggs decrease.
Menopause marks the absolute end of the reproductive lifespan. The age of menopause varies between women but usually occurs between the ages of 45 and 55 years. Pregnancies in the ten years leading to menopause are rare.
The age at which women are having their first baby is increasing in Australia and elsewhere. This in turn increases the risk of age-related infertility. Women who worry about their "biological clock" ticking away, particularly single women, want to know how long they can wait without jeopardising their chance of having a baby.
Can women tell how long they have?
Women are increasingly having the so-called "egg timer" test to get an idea of how much longer they have to achieve pregnancy. The authors of a recent Australian study recommend women in their late 20s have the "egg timer" test at regular intervals to monitor their fertility potential.
This is a blood test that measures a woman's level of anti-müllerian hormone (AMH) which is linked to the number of eggs remaining in a her ovaries. Higher levels mean more eggs are present, which theoretically means a higher fertility potential.
But the "egg timer" test does not provide information about the quality of the eggs, which mostly depends on a woman's age.
Relying on the "egg timer" test for pregnancy planning can give women with normal or high readings a false sense of security about postponing childbearing and women with low readings unnecessary worry about their ability to have children. This might lead them to pay the significant cost associated with egg freezing.
More education about age and fertility is needed
Most Australians overestimate the reproductive lifespan by about ten years. To improve the chance of people achieving their parenthood goal, particularly if this is to have two or more children, more awareness about the impact of age on fertility is needed.
The Australian government funded "Your Fertility" program provides up-to-date, accessible and evidence-based information about the factors that affect fertility. Primary health care providers also have an important role to play in educating people about the limitations of fertility.
Men need to step up
Discussions about timing of childbearing tend to focus on women but research shows one of the main reasons for later childbearing is women have trouble finding a male partner willing to commit to parenthood.
While men almost universally value parenthood, want and expect to become fathers, and aspire to have at least two children, most have inadequate knowledge about the limitations of female and male fertility and overestimate the chance of spontaneous and assisted conception.
Since childbearing and parenthood are shared endeavours, men who want children and have a partner need to be active participants in childbearing decision-making and avoid deferring the decision to have children to a time when the chance of achieving a pregnancy is diminished.
Options for women who want children but don't have a partner
Depending on their personal circumstances and age, women who want children but don't have a partner can consider the following "reproductive life planning" options:
• striving to be in the best possible health improves fertility. This includes not smoking, being in the normal weight range, exercising regularly and eating a balanced diet
• having a discussion early in a new relationship about if and when to have children to avoid disappointment years down the track
• deciding to be a single mum and using donor sperm to conceive
• freezing eggs to improve the chance of having children later in life. This is an expensive option with no guarantee of success. Many women with stored eggs conceive without using them and one in six women regret freezing their eggs
• while there is currently no reliable test of fertility potential to tell women for how much longer they're likely to be able to conceive, there is hope longitudinal studies currently underway will be able to identify women at risk of reduced ovarian reserve based on repeated testing.
Karin Hammarberg is a Senior Research Fellow, Jean Hailes Research Unit, School of Public Health & Preventive Medicine at Monash University.
Luk Rombauts is an Adjunct Clinical Professor at Monash University.
This article first appeared on The Conversation.