Archive · 29 Sep 2026
Study Finds Pregnancy Brain Fog Linked To Hormonal Circuit
Many pregnant women say they sometimes forget things or lose track of conversations.
Scientists call this experience pregnancy brain or baby brain.
A new study suggests that hormones may help explain it.
In mice, high levels of oestrogen changed communication between two brain areas involved in memory.
When researchers turned off this communication pathway, the mice’s memory problems disappeared.
They also studied 70 women and found that some memory skills were weaker late in pregnancy.
However, the human results show a link, not definite proof that oestrogen caused the changes.
The findings do not mean pregnancy makes people less intelligent.
Memory changes usually improve after childbirth.
Researchers found that high oestrogen levels affected a brain pathway involving the hypothalamus and hippocampus in mice.
The pathway altered hippocampal activity, which is important for learning and memory.
A study of 70 pregnant and non-pregnant women found weaker performance on some memory tests during late pregnancy.
Higher circulating oestrogen levels were associated with poorer performance, but the human findings do not prove causation.
The changes appear to affect specific memory functions, are generally temporary, and do not indicate lower overall intelligence.
- Who
- Researchers led by Zheng Sun and Yanlin He studied mice and 70 pregnant and non-pregnant women.
- What
- The study examined pregnancy-related memory changes and found a possible link to high oestrogen levels and a hypothalamus–hippocampus brain pathway.
- When
- The changes were examined at different stages of pregnancy, with some effects observed during late pregnancy; the study was published in Science Bulletin.
- Where
- The research involved laboratory experiments in mice and memory testing of women; the articles do not specify a location.
- Why
- Researchers sought to explain the forgetfulness and mental fog reported by many pregnant women.
Biological Explanation
Scientific Caution
What causes pregnancy brain?
Biological Explanation
The mouse experiments suggest that high oestrogen activates hypothalamus neurons, which reduce hippocampal activity and produce memory problems through a specific brain pathway.
Scientific Caution
The human study found only an association between oestrogen levels and memory performance. The pathway cannot be directly tested in pregnant women in the same way, so the animal mechanism has not been confirmed in humans.
Meaning of the memory changes
Biological Explanation
The findings offer a biological explanation for forgetfulness that many pregnant women have reported and suggest the effects involve particular memory tasks.
Scientific Caution
The researchers say more work is needed, and the findings do not establish a general cognitive decline or reduced intelligence.
- Publication
- Science Bulletin
- Human participants
- 70 women at different stages of pregnancy, along with non-pregnant women
- Reported prevalence
- Around 80% of pregnant women report some cognitive change, based mainly on self-reports
- Hormone studied
- Oestrogen, which rises sharply during pregnancy and peaks in later pregnancy
- Brain pathway
- A connection between the hypothalamus and hippocampus
- Observed effect
- Some memory functions were weaker during late pregnancy
- Duration
- The changes are generally temporary and tend to improve after childbirth