The Australian analysis of 14 research studies around the world since 1990 provides "clear-cut findings" that pregnancy impairs memory for up to 80 per cent of pregnant women and new mothers.
The study, by the University of NSW and Australian Catholic University, compared the memory performances of more than 1000 pregnant women, new mothers and healthy, non-pregnant females.
"The results indicate that pregnant women are significantly impaired on some, but not all, measures of memory and, specifically, memory measures that place relatively high demands on executive cognitive control may be selectively disrupted," the study said.
"The same specific deficits associated with pregnancy are also observed postpartum."
But one of the study's authors, Julie Henry, a psychology researcher at the University of NSW, said the impairment was "very, very subtle".
The cause is not known and theories include hormonal changes and sleep deprivation.