Women who have worked in temporary jobs are less likely to have had a child before the age of 35, new research published in a medical journal suggests.

In data published by the journal Human Reproduction, researchers from the University of Adelaide in Australia interviewed 663 women between the ages of 32-35, asking them for retroactive data about major life events from the time they were 15 years old and onward.

All the women in the survey were born in the same hospital in Adelaide between 1973 and 1975 and were interviewed between 2007 and 2009, meaning they were at least 32 years old but no older than 35 when interviewed.

If a woman was studying full time at any point in that 20-year window, she was considered to be a student and employment during this period was not taken into account.

'Regardless of their socioeconomic circumstances, women generally aspire to economic security prior to starting a family.' - Human Reproduction report

The research team led by professor Vivienne Moore found that at the time of the interviews, 67 per cent (442 of the 663 women) had given birth to at least one child by the age of 35.

But the researchers found that the likelihood of having a child before the age of 35 was reduced for every year spent in temporary or casual employment. One year of casual work was associated with an eight per cent reduction in the likelihood of a first baby compared to women who had had no temporary job experiences.

The likelihood of having a baby before 35 was reduced by 23 per cent for those who had spent at least three years in some sort of cycle of temporary work and by 35 per cent after five years.

Numbers steady across salary ranges

The paper's findings are consistent with other statistics that show professional, educated women are waiting until later in life to have children, presumably so that they are closer to financial security before starting a family. But the report's authors stress that the likelihood of delaying motherhood was linked to temporary work among all socioeconomic levels.

"Our findings suggest that, regardless of their socioeconomic circumstances, women generally aspire to economic security prior to starting a family," the paper reads. "This finding is important because it challenges the pervasive media representations of delayed childbirth as a phenomenon arising from highly educated women choosing to delay motherhood to focus on their careers."

The paper also found that 61 per cent of women who had received some sort of university degree spent at least one year in a state of temporary employment after graduation.

"This highlights the fact that temporary employment is no longer the sole domain of low-skilled, poorly paid people," University of Adelaide lecturer Dr. Lynne Giles said.

The report cautions that while researchers analyzed women's employment history, they did not collect data on their partners. They did, however, take the partner's education into account, and they plan to investigate the employment history of both the women and the men in future research.