'Momnesia' Is Real: Why Pregnancy Could Temporarily Change the Way Your Brain Works
Pregnancy can bring a long list of physical changes, but some women also notice something less visible: forgetting names, losing track of conversations, or walking into a room and forgetting why they went there.
Often called 'momnesia', 'pregnancy brain' or 'baby brain', these temporary cognitive changes have been reported for decades. Now, scientists say they may have identified a biological mechanism that could help explain why pregnancy affects memory.
A new study published in Science Bulletin found that sustained high levels of oestrogen during pregnancy may alter a specific brain circuit involved in memory. The researchers found evidence in mice and also observed a relationship between higher oestrogen levels and poorer performance on some memory tests in pregnant women.
How Pregnancy Hormones Could Affect Memory
Oestrogen rises substantially during pregnancy and reaches particularly high levels by the third trimester. Researchers found that these hormonal changes may influence neurons in the hypothalamus, a brain region involved in regulating several essential body functions.
In experiments involving mice exposed to pregnancy-like levels of oestrogen, researchers found increased activity in GABAergic neurons in the hypothalamus. These neurons then suppressed activity in the hippocampus, a region that plays a central role in learning and memory.
The result was temporary impairment in several memory tasks. When scientists experimentally switched off the pathway connecting the hypothalamus and hippocampus, the memory problems disappeared in the mice. Activating the same pathway, meanwhile, was enough to impair memory even without elevated oestrogen.
The findings suggest that pregnancy-related forgetfulness may involve changes in how specific brain circuits communicate rather than a broad decline in cognitive ability.
Is 'Momnesia' Actually Common?
The researchers assessed memory in 70 women at different stages of pregnancy and found that memory changes became more apparent later in pregnancy. Higher circulating oestrogen levels were also associated with poorer performance on several memory-related measures.
However, the human findings do not prove that oestrogen directly causes memory problems. The researchers could not experimentally manipulate or directly examine the same neural circuit in pregnant women, meaning the strongest evidence for the mechanism comes from the animal experiments.
Self-reported cognitive symptoms appear to be widespread. The researchers cited estimates suggesting about 80% of pregnant women notice some form of cognitive change, although this figure reflects people's perceptions rather than objective memory testing.
Previous research cited in Springer Nature Link has also found evidence of pregnancy-related cognitive changes. A systematic review of 31 studies involving 1,596 pregnant women and 1,450 non-pregnant controls found that pregnancy was modestly associated with differences in verbal memory and attention.
Does Pregnancy Permanently Change the Brain?
The changes associated with 'momnesia' do not necessarily mean pregnancy causes permanent cognitive decline.
The researchers described the memory effects as temporary and task-specific, with symptoms generally improving after childbirth. Separate research has also shown that pregnancy can produce measurable changes in brain structure and connectivity.
A 2024 National Institutes of Health-highlighted study that repeatedly scanned one woman throughout pregnancy found widespread changes in grey matter, cortical thickness, and white matter, with some changes partially reversing after birth. The researchers described pregnancy as a period of significant neuroplasticity, meaning the brain adapts and reorganises in response to changing demands.
For women experiencing occasional forgetfulness during pregnancy, these findings offer a biological explanation rather than evidence that they are becoming less intelligent. Persistent, severe, or otherwise concerning cognitive symptoms should still be discussed with a healthcare professional, particularly if they interfere substantially with daily life.