How a woman's brain changes during pregnancy: study results baffle scientists

Pregnancy causes huge changes in a woman's body - hormonal, cardiovascular, respiratory, gastrointestinal, urinary and more. And, as the new study shows, the brain also undergoes major changes, some fleeting and others more persistent.

Scientists said they have, for the first time, mirrored the changes that occur when a woman's brain reorganizes in response to pregnancy. The study documented a widespread decrease in the volume of cortical gray matter, the wrinkled area comprising the outer layer of the brain, as well as an increase in the microstructural integrity of white matter deeper in the brain. Both changes coincided with increased levels of the hormones estradiol and progesterone, Reuters writes.

Gray matter consists of the bodies of nerve cells in the brain. White matter is made up of bundles of axons - long, thin fibers - of nerve cells that transmit signals over long distances in the brain.

The study, the first of its kind, was based on a single subject: cognitive neuroscientist Elizabeth Hrastil, a University of California, Irvine, cognitive neuroscientist and study co-author who gave birth for the first time to a healthy baby boy who is now 4.5 years old. At the time of the study, Hrastil was 38 years old and is now 43. The results of the study are generated from brain scans taken 26 times, starting three weeks before conception, during the nine months of pregnancy, and two years after giving birth.

Researchers said that since the study was completed, they have observed the same pattern in several other pregnant women who have undergone brain scans as part of an ongoing research initiative called the Maternal Brain Project. They aim to increase the number to hundreds.

"It's very shocking that in 2024 we have almost no information about what happens in the brain during pregnancy. This research paper opens up more questions than it answers, and we are only touching the surface of those questions," added Chrastil.

The scans showed a reduction in gray matter of about4 percent in about 80 percent of the brain regions studied. A small rebound after delivery did not return the volume to gestational levels. The scans also showed an increase of about 10% in white matter microstructural integrity, an indicator of the health and quality of connections between brain regions, peaking at the end of the second trimester and beginning of the third trimester and then returning to pre-pregnancy levels.

"The maternal brain undergoes choreographic changes during pregnancy, and we can finally observe the process in real time. Prior studies have taken pictures of the brain before and after pregnancy. But we've never seen the brain while carrying a baby," said University of California, Santa Barbara neuroscientist Emily Jacobs, senior author of the study.

The researchers said it's unclear whether the loss of gray matter is a negative factor.

"This change may indicate a fine-tuning of brain circuits. It seems to happen to all young people as they move through puberty and their brains become more specialized. Some of the changes we observed may also be a response to the high physiological demands of pregnancy itself, demonstrating how adaptive the brain can be," said Laura Pritchett, a doctoral student and lead author of the study at the University of Pennsylvania.

Scientists hope to investigate in the future how variations in these changes can help predict phenomena such as postpartum depression and how pre-eclampsia, a serious blood pressure condition that can develop during pregnancy, can affect the brain.

Chrastil said she didn't realize the data about the changes in her brain during the study and didn't feel anything different.

"Some people talk about 'mommy brain' and things like that. And I didn't really feel any of that," she added, referring to the fogginess of mind that some pregnant women experience.

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