A study of 2,500 women found no difference in their brainpower before and during their pregnancies
The popular belief that pregnancy addles women's brains is a myth, a comprehensive study suggests.
Mothers claim to have suffered 'baby brain' or 'preg head', characterised by lapses in memory or logical thinking.
But researchers who tracked 2,500 women over ten years found no difference between their brainpower before and during their pregnancies.
In fact, the scientists believe, pregnancy and motherhood could actually improve women's mental abilities - and the improvement may be permanent.
Previous studies have claimed that pregnant women's brains decline in size and that they consistently perform worse than other women on tests for memory and verbal skills.
They have suggested that the difference could be as great as comparing the mental ability of someone aged 20 with someone aged 60.
But Professor Helen Christensen, of the Australian National University in Canberra, said her study is superior to previous research because it compares the same women before and during pregnancy.
'Women often report problems with memory and reasoning after they become pregnant,' she said. 'But the latest findings from our decade-long study, the most in-depth to look at this issue, has proven they do not.'
The researchers studied 2,500 women aged from 20 to 24, first in 1999 and then again in 2004 and 2008.
'We found that women who were pregnant during the second or third batch of interviews performed the same on tests of logic and memory as they did before, and there was no difference between the pregnant women and the controls,' she said.
'It really leaves the question open as to why women think they have poor memories, when the best evidence we have is that they don't.
'Perhaps women notice minor lapses in mental ability and then attribute it to being pregnant because that is the most significant thing in their mind at the time.
'Or sleep deprivation could mask the positive cognitive effects.'