One in every four women with a history of infertility can still conceive without treatment, says new research.

The study, led by Danielle Herbert, from the University of Queensland School of Population Health, reveals that women who have been clinically diagnosed as infertile after 12 months of unsuccessfully trying for a baby may actually just need longer to conceive.

"Many women aged up to 36 years with a history of infertility, especially those who have already had a baby, can achieve spontaneous conception and live birth without using fertility treatment indicating they are sub-fertile rather than infertile," the journal Fertility and Sterility reports.

The study shows that one in every four Australian women, aged 28-36 years, who reported a history of infertility had a baby without using fertility treatment, and a further one in every four had a baby after undergoing fertility treatment, which included 'In vitro fertilisation(IVF)' or fertility hormones, such as Clomid.

Half of those women who had not used treatment had already had a baby prior to reporting infertility. “ The strength of this study is the inclusion of all women with a self-reported history of infertility,” Herbert said.

The research is part of the Australian Longitudinal Study on Women's Health which has followed more than 8,000 women since 1996. This latest data comes from surveys conducted in 2006 and 2009.