A study by Jean Hailes for Women's Health has found that women's childbearing desires are influenced by a host of practical factors that are sometimes beyond their control.

Lead author Sara Holton, from the Monash University School of Public Health, said women's fertility decision-making was affected by issues such as relationship status as well as financial and health concerns.

Dr Holton said that previous research has tended to explain women's childbearing decisions as rational, voluntary and focused on ''costs''.

''There's been this assumption that women are able to choose when and if they can have children,'' she said.

The total fertility rate for Australia was 1.89 babies per woman last year but it has been below the replacement level of 2.1 since 1976.

The study surveyed 569 Victorian women between 30- and 34-years-old, as the age group with the highest fertility rate in Australia.

Some 80 per cent said they had fewer children than they wanted. But despite the fact the women were still in their reproductive years, 54 per cent said that they were unlikely to have more children.

The study, first published in the Journal of Population Research, found that women's fertility was influenced by a wide range of personal factors, such as not having a partner, not having a stable relationship or with a partner that did not want children.

''They haven't lost interest in children but they're facing barriers to motherhood,'' Dr Holton said.

The study also found that women were influenced by education debts and housing concerns, such as wanting to buy a house or find stable accommodation before having a child.

Even for women who already had children, financial factors - including the need to find a bigger house - played into their thinking.

''[They said] if the circumstances are different then they'd like to have more children,'' Dr Holton said.

Other women surveyed said their decision-making was influenced by their health, including concerns they might pass on a genetic condition.

Queanbeyan's Gwen Keith, 36, is a full-time mother to her son Corbin, 17 months. Ms Keith said she and husband Evan Walters, 32, would like to have another child but Corbin will be an only child for health and financial reasons.

Corbin was born through IVF and the family cannot afford to go through the process again. ''It's not necessarily in our hands,'' Ms Keith said.

Ms Keith, who has put her career as a nanny on hold to care for her son, said their decision also meant Corbin could have more opportunities.

''We'd like to be able to provide for him,'' Ms Keith said, noting that she was already taking Corbin to swimming and gym lessons and hoped to send him to whatever school suited him best.

Not having more children also meant the family could get by with a smaller house and car.