It has been called "baby brain" and "placenta brain" - but now the commonly held idea that pregnant women have misplaced their memory has gained scientific backing. A series of tests comparing pregnant women with those not carrying a baby has indicated that the condition erodes a woman's ability to remember what she has been told.

This is probably only temporary and is thought to be related in part to sleep deprivation. Melbourne registrar Dr Lenore Ellett yesterday presented findings of a study she did with sleep scientist Danielle Wilson to the Auckland conference of the Royal Australian and New Zealand College of Obstetricians and Gynaecologists.

They performed standard psychology tests of auditory and visual memory on 90 women: 30 were in the first third (trimester) of pregnancy; 30 in the last third; and 30 were not pregnant. No variation between the groups was found in visual memory. But in the listening tests, when compared to women who were not pregnant, those in the first trimester performed slightly worse - and those in the third trimester performed significantly worse.

Dr Ellett said that because it was known that sleep deprivation could lead to memory loss, the study's hypothesis was that sleep deprivation may be a factor affecting memory during pregnancy. The participants' sleep was measured too, but those results were not available yet.

Other possible causes were hormonal changes and psychological and emotional issues - the "momentous life change" of being pregnant. When asked if memory loss in pregnancy might be permanent, Dr Ellett, who was also a pregnant participant of the study, said: "I don't think so. It's related to what's going on at the time."

She said the findings were important, because doctors usually provided only verbal advice to pregnant patients. "Clinicians need to be aware that information given orally to pregnant women may not be retained as well as written information."