Pregnancy 'Brain Fog' Is Real, Study Finds, And Scientists May Know Why

Forgetfulness during pregnancy, often described as "baby brain", "pregnancy brain" or "momnesia", may have a biological explanation, scientists say. A new study has found that high levels of oestrogen during pregnancy can affect a specific brain circuit involved in memory. The findings suggest that the mental fog and forgetfulness reported by many pregnant women may not simply be a matter of tiredness or stress.

Researchers found that sustained high oestrogen levels affected a pathway connecting the hypothalamus, a part of the brain involved in regulating several body functions, with the hippocampus, which plays a key role in learning and memory.

The study was published in the journal Science Bulletin.

What is 'baby brain'?

Many pregnant women report having trouble remembering names, losing track of conversations, forgetting why they entered a room or misplacing everyday items.

Researchers say around 80% of pregnant women report some form of cognitive change during pregnancy. However, this figure is largely based on people's own reports rather than formal memory tests.

The changes are generally temporary and tend to improve after childbirth.

The new research suggests that pregnancy does not cause a general decline in intelligence. Instead, certain types of memory appear to be affected.

"It is not serious or medically disabling," Zheng Sun, one of the study's leaders, told Reuters, while noting that the changes can affect everyday life and confidence.

How do pregnancy hormones affect memory?

Oestrogen is an important hormone during pregnancy. Its levels rise sharply and reach their highest levels during the later stages of pregnancy.

In experiments involving mice, scientists found that high levels of oestrogen increased the activity of certain neurons in the hypothalamus. These neurons then reduced activity in the hippocampus, affecting memory.

The researchers also identified the role of oestrogen receptors in this process.

When the scientists switched off the specific pathway connecting the hypothalamus to the hippocampus, the memory problems in the mice disappeared. Activating the same pathway, meanwhile, caused memory problems even without raising oestrogen levels.

This suggests that the brain circuit itself may be an important link between high oestrogen levels and temporary memory problems.

What did the study find in pregnant women?

The researchers also studied 70 women at different stages of pregnancy, along with women who were not pregnant.

They found that some memory functions were weaker during late pregnancy and that higher circulating oestrogen levels were associated with poorer performance on several memory tests.

However, scientists stressed that the human findings show an association, not proof that oestrogen directly causes the memory changes.

The specific brain circuit identified in the mouse experiments cannot be directly tested in the same way in pregnant women.

"This provides human evidence consistent with the mechanism we identified in mice," researcher Yanlin He said, according to Reuters. But the researchers also noted that the human results do not establish the same level of cause and effect as the animal experiments.

Does pregnancy make women less intelligent?

No. The researchers say the findings do not suggest a general reduction in intelligence.

Instead, the effects appear to be limited to particular cognitive tasks, especially some forms of memory. The changes are also generally temporary.

The findings offer a possible biological explanation for a phenomenon that many women have described for years. They also provide scientists with a clearer picture of how major hormonal changes during pregnancy can influence the brain.

For now, the researchers say more work is needed to establish whether the same brain circuit identified in mice operates in the same way in pregnant women.