“OOPS, I left the baby on the bus.” The old jokes about pregnancy, or placenta, brain now have hard science to back them up with a West Australian researcher finding the first physiological link between a key pregnancy hormone and short-term memory loss.

Until now, only widespread anecdotal evidence from mothers-to-be supported claims that pregnancy caused forgetfulness, but researcher Anna Baron has replicated the effects in the lab.

WA researchers hope the study will help lead them to a treatment for another condition associated with memory loss and hormonal changes, Alzheimer’s disease.

“There have been plenty of epidemiological studies showing a link between pregnancy and memory loss, but now I have some pretty good evidence of the physiological basis for this,” Ms Barron says.

Working with renowned Alzheimer’s scientist Professor Ralph Martins, Ms Barron treated mice for 17 to 50 days with a hormone palette that mimicked the effects of both pregnancy and menopause.

She used human chorionic gonadotropin (hCG) and luteinizing hormone, both of which are sharply spiked in pregnancy.

Levels of these hormones also rise with ageing and have been shown to increase the production of toxic beta amyloid protein, which forms the brain plaques that cause Alzheimer’s.

Ms Barron discovered changes in the mice’s working, or short-term, memory, and motor skills. She also examined anxiety levels, which can be an early predictor of Alzheimer’s.

Of the two hormones, hCG produced by far the more profound results.

“The higher the hCG, the more marked the effect,” she says.

“Lower doses showed a trending effect (on motor skills and memory) but higher does – those in keeping with the spike of pregnancy – showed a marked effect. The doses over a longer period showed impairment in memory and changes in motor skills that have parallels with Alzheimer’s.”

The study, she says, offers new hope for Alzheimer’s sufferers, because overwhelmingly women with “pregnancy brain” return to a normal memory pattern after giving birth.

“This is really the first study that shows, long term, the effect of these hormones is reversible,” she says.

“Most of these women after pregnancy go back to normal. There are some case studies where women who have had children say they have never been the same, but because there are so many other things that go on in women’s lives that are assisting that process (of memory loss), it’s hard to make a direct link. Scientists have to take into account that changes in sleep patterns and being busy with children could be contributing to this effect.”

She says an Alzheimer’s treatment based on controlling lutenizing hormone has just completed a successful phase two clinical trial in the United States. The new drug is taken in conjunction with currently available medication for the disease.

“I think in the long term this type of hormone treatment will be tailored for individuals,” she says. “Because everyone is different and ideally should be treated case by case.”

Ms Barron presented her research at this week’s Australian Society for Medical Research symposium at Curtin University of Technology, and will be speaking at an international conference in the US later this year.