SYDNEY, Feb 5, 2010 (AFP) - Australian researchers said on Friday they had debunked the myth that a women's ability to think was impaired by pregnancy and mothering a newborn - a condition commonly referred to as "baby brain".

An Australian National University team conducting a 20-year population study on health and ageing analysed the mental function of a group of women before and during pregnancy and in the early stages of motherhood.

"We didn't find any difference between the women before and after pregnancy, or before and after motherhood, and there were no differences between the non-mothers and the mothers, and the pregnant women," lead researcher Helen Christensen told AFP.

The women were given memory and cognitive speed tests three times over eight years as part of the "Path Through Life" study, which is tracking the mental health of a random sample of 7,500 Australians over 20 years.

Christensen said the findings were unique because the women were not told they were being tested for a pregnancy study when they signed up and it was the first time researchers could make a comparison with pre-conception scores.

"You don't have necessarily the biases that you might have if you are just doing a study where you recruit women to a pregnancy study," she said.

"When they're doing the cognitive test they don't know that it's out to prove that they've lost their marbles or otherwise."

According to the study, which was published in the British Journal of Psychiatry, pregnant women were frequently warned about the possibility of short-term memory problems, a condition guidebooks described as "baby brain" or "placenta brain".

"These views are supported by scientific research evidence and systematic reviews," it said.

While the study had found some limited impact on cognitive speed in late pregnancy, Christensen said the results showed that carrying a baby had "pretty much no permanent effects" on a woman's mental function.

"I think that people have the tendency to blame the fact that they're pregnant on normal lapses of memory which happen all the time to us anyway," she said.

Christensen said the findings showed "'placenta brain' is not inevitable, and that perceptions of impairment may reflect emotional or other unknown factors."

"Our results challenge the view that mothers are anything other than the intellectual peers of their contemporaries," she said.