Pregnant women may have long suspected it, but a new Australian study has confirmed that carrying a baby can make mothers-to-be more forgetful.
Research by Australian scientists has found that a woman's memory can be impaired for at least a year after giving birth, although the effects are minor and mainly concern unfamiliar or demanding tasks.
"The memory deficits many women experience during and after pregnancy are pretty much like the modest deficits you'd find when comparing healthy 20-year-olds with healthy 60-year-olds," researcher Julie Henry said.
The Australian study analysed the results of 14 different studies from around the world which tested the memory performances of more than 1,000 pregnant women, mothers and non-pregnant women.
It found that pregnant women performed significantly worse on some, but not all aspects of the test.
The hardest tests for the pregnant women were those which involved new or difficult tasks.
"Regular, well-practised memory tasks -- such as remembering phone numbers of friends and family members -- are unlikely to be affected," said the Australian Catholic University's Associate Professor Peter Rendell, who conducted the study with Henry.
"It's a different story, though, when you have to remember new phone numbers, people's names or hold in mind several different pieces of information, such as when multi-tasking."
The study, published in the Journal of Clinical and Experimental Neuropsychology, also suggests that so-called "baby brain" is still in evidence a year after childbirth.
But because none of the studies has gone beyond that time, it could not determine whether the problem is permanent.
Scientists are also baffled as to why a woman's memory would suffer at such an important time.
"Although we have no experimental evidence for it, our suspicion is that lifestyle factors are relevant," said Henry, a psychology researcher at the University of New South Wales.
"In pregnancy your normal routines are disrupted and you can suffer sleep deprivation after the birth -- we know from other research that either of those things can affect cognitive performance."