Study shows how a woman's brain reorganises during pregnancy

WASHINGTON — Pregnancy triggers vast changes in a woman's body — hormonal, cardiovascular, respiratory, gastrointestinal, urinary and more. And, as a new study reveals, the brain undergoes major changes too, some fleeting and others more enduring.

Researchers said on Monday (Sept 16) they have for the first time mapped the changes that unfold as a woman's brain reorganises in response to pregnancy, based on scans carried out 26 times starting three weeks before conception, through nine months of pregnancy and then two years postpartum.

The study documented a widespread decrease in the volume of cortical grey matter, the wrinkled area that comprises the brain's outermost layer, as well as an increase in the microstructural integrity of white matter located deeper in the brain. Both changes coincided with rising levels of the hormones oestradiol and progesterone.

Grey matter is comprised of the cell bodies of the brain nerve cells. White matter is made up of the bundles of axons — long, thin fibres — of the nerve cells that transmit signals in long-distance connections across the brain.

The study, the first of its kind, was based on a single subject: University of California, Irvine cognitive neuroscientist and study co-author Elizabeth Chrastil, a first-time mother who gave birth to a healthy boy, now four and a half years old. Chrastil was 38 during the study, and 43 now.

The scientists said that since the study's completion they have observed the same pattern in several other pregnant women who have undergone brain scans in an ongoing research initiative called the Maternal Brain Project. They aim to expand the number into the hundreds.

"It's pretty shocking that in 2024 we have hardly any information about what happens in the brain during pregnancy. This (research) paper opens up more questions than it answers, and we are just scratching the surface of these questions," Chrastil added.

The scans showed a reduction averaging about four per cent in grey matter in roughly 80 per cent of the brain regions studied. A small rebound postpartum did not return the volume to pre-pregnancy levels.

The scans also showed an increase of about 10 per cent in white matter microstructural integrity, a measure of the health and quality of the connections between brain regions, peaking late in the second trimester and early in the third trimester, then returning to pre-pregnancy status postpartum.

"The maternal brain undergoes a choreographed change across gestation, and we are finally able to observe the process in real time," said University of California, Santa Barbara neuroscientist Emily Jacobs, senior author of the study published in the journal Nature Neuroscience.

"Previous studies had taken snapshots of the brain before and after pregnancy. But we've never witnessed the brain in the midst of this metamorphosis," Jacobs added.

The researchers said it is not clear that the loss of grey matter is a bad thing.

"This change could indicate a fine-tuning of brain circuits, not unlike what happens to all young adults as they transition through puberty and their brain becomes more specialised.

Some changes we observed could also be a response to the high physiological demands of pregnancy itself, showcasing just how adaptive the brain can be," University of Pennsylvania postdoctoral scholar and study lead author Laura Pritschet said.

The researchers hope in the future to examine how variation in these changes could help predict phenomena such as postpartum depression and how preeclampsia, a serious blood pressure condition that may develop during pregnancy, could affect the brain.

Chrastil said she was not aware during the study of the data showing her brain changes and did not feel any different.

"And so, you know, now there's some distance to be able to say, 'Okay, well, that was a wild ride,'" Chrastil said.

"Some people talk about Mommy Brain and things like that," Chrastil added, referring to the mental fogginess some pregnant women experience. "And I didn't really experience any of that."

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