(CNN) -- Science has now confirmed what expectant moms already know: Carrying a baby makes them more forgetful.

Researchers suspect that pregnant women's forgetfulness stems from hormone shifts and lifestyle changes.

A recent study by two Australian researchers has found that pregnant women do experience a slight loss of memory -- and in many cases, the forgetfulness continues after birth.

The memory loss is subtle, and usually involves unfamiliar or demanding tasks, Dr. Julie Henry, one of the authors of the study, told CNN on Tuesday.

"What we found is that memory tasks which are more challenging or more novel, or those that would require multitasking -- these types of tasks are likely to be disrupted," said Henry, a senior lecturer in Sydney's University of New South Wales.

For example, a pregnant woman is more likely to forget a new telephone number, but she is able to recall a number she has dialed many times before, Henry said.

Henry and her colleague, Dr. Peter Rendell of Melbourne's Australian Catholic University, analyzed 14 studies from around the world that tested the memory performances of more than 1,000 women -- expectant women, mothers and non-pregnant females.

The study, published in the Journal of Clinical and Experimental Neuropsychology, found that the memory loss can extend up to a year after birth.

The researchers could not establish whether the forgetfulness lasts longer because none of the research they analyzed went beyond the one-year observational period.

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Henry and Rendell said that more research is needed to determine what causes the loss at such a critical period of a woman's life. It may result from hormonal changes or from a lifestyle shift, Henry said.

"You're probably more preoccupied with the upcoming birth and (how) your whole life is going to be changing," she said. "You're going to have more difficult sleeping. And other studies have shown that sleep deficiency definitely disrupts cognitive performance. There's no reason to think it won't do so during pregnancy."

So, has Henry experienced the syndrome firsthand?

"I haven't yet," she said, laughing. "It hasn't put me off." E-mail to a friend