Australian women who take maternity leave pay a financial penalty even three years after their return to work, research has found.
They receive a lower hourly pay rate than other female workers with no career break even though both groups had previously been on the same hourly pay scale.
''The women are going backwards because they took time out of the workforce while their colleague are progressing down the career path,'' said David Baker, a research fellow at the Australia Institute.
After one year back at work their hourly pay rate was 4.4 per cent less than their once-similarly paid colleagues, and by the third year they were getting 12.3 per cent less.
Mr Baker said the findings had implications for the federal government's new paid parental leave scheme, which began in January. The means-tested scheme gives most parents with the option of 18 weeks' leave paid at the minimum wage.
''The new system does not address the potential future disadvantage for women returning to work following maternity leave,'' he said. ''Other evidence shows the greatest wage disparity occurs 10 years after childbirth.''
The study, detailing the ''hidden cost of maternity leave'', found women paid an average ''wage penalty'' of $1566 in 2009 because of slower wages growth after returning from maternity leave. Their loss is equivalent to about three weeks' paid parental leave.
''In effect, due to the wage penalty women will be receiving just 15 weeks of paid parental leave, not 18,'' he said.
Mr Baker's research is based on tracking wages growth for 203 women who returned to work after maternity leave between 2002 and 2009 compared to wages growth for women who kept working.
The sample is drawn from the Household, Income and Labour Dynamics in Australia (HILDA) survey, which has gathered data on thousands of Australians since 2001 to reveal their changing circumstances.
The women who took leave on average experienced a decrease in their hourly pay rate while their colleagues received a 4 per cent rise.
Mr Baker said it was not possible to determine how different lengths of maternity leave affected wages growth. All the women in the survey had returned to work within a year. It was also not possible to tell if they had returned to their previous workplaces.
''The paid parental leave scheme is very welcome, especially for the majority of women who are working part-time or in low-paid jobs and didn't have access to paid leave before,'' Mr Baker said. ''But complementary policies need to be developed, like keeping women more connected to to the workforce during leave.''
National Federation of Australian Women spokeswoman Marie Coleman said long absences from work played havoc with earning capacity.
Increasing the take-up of parental leave by fathers would help change workplace culture, and this would become easier when dedicated partner leave was introduced next year.
Do you think mums in the workplace are discriminated against? Have your say on the Essential Baby forums.