Pregnancy causes major changes in a woman’s body, including hormones, the heart and blood vessels, breathing, digestion and excretion, but a new study has also revealed that the brain undergoes major changes, some of which are temporary and some of which last for periods.
Researchers said Monday they were able to map for the first time the changes that occur when the brain reorganizes itself in response to pregnancy, based on 26 scans over a broad period starting from three weeks before conception through nine months of pregnancy and up to two years after birth.
The study documented a broad reduction in the volume of gray matter known as the cerebral cortex, the wrinkled outer layer of the brain, as well as an increase in the microstructural integrity of the brain’s inner white matter (a measure of the health and quality of connections between brain regions). Both changes coincided with higher levels of the hormones estradiol and progesterone.
Grey matter is made up of the cell bodies of neurons in the brain, while white matter is made up of bundles of axons—the long, thin fibers—of neurons that transmit signals long distances through the brain.
The study, the first of its kind, was based on a single case: Elizabeth Krastel, a cognitive neuroscientist at the University of California, Irvine, who co-authored the study.
Krastel is a first-time mother who gave birth to a healthy 4-and-a-half-year-old boy. She was 38 when she was studied, and is now 43.
Brain scans
Since completing the study, the authors said, they have seen the same pattern in several other pregnant women who have had brain scans as part of an ongoing research initiative called the Maternal Brain Project. They aim to expand the project’s caseload into the hundreds.
“It’s shocking that in 2024 we have so little information about what happens in the brain during pregnancy,” said Crastel. “This study opens up more questions than it answers, and we’re only just beginning to answer them.”
The scans showed an average 4% shrinkage of gray matter in about 80% of the brain regions studied. A slight rebound after birth did not return cortical volume to pre-pregnancy levels.
The scans also showed a roughly 10 percent increase in the integrity of white matter microstructure — a measure of the health and quality of connections between brain regions — which peaked in the late second and early third trimesters, then returned to its pre-pregnancy state after birth.
“The mother’s brain undergoes a change specific to pregnancy, and we are finally able to monitor the process in real time,” said Emily Jacobs, a neuroscientist at the University of California, Santa Barbara, and senior author of the study published in the journal Nature Neuroscience.
“Previous studies have taken images of the brain before and after pregnancy. But we have never observed the brain during this transition,” she added.
It is not clear if, the researchers said. what The loss of gray matter was bad.
Fine tuning of brain circuits
“This change is likely a sign of fine-tuning of brain circuits, not unlike what happens to all young people as they transition into adulthood when their brains become more specialized,” said Laura Pritchett, a graduate student at Penn State and co-author of the study. “Some of the changes we observed may also be a response to the high physiological demands of pregnancy itself, showing how adaptable the brain is.”
In the future, researchers hope to study how variation in these changes might help predict conditions such as postpartum depression and how preeclampsia, a dangerous condition of high blood pressure that can develop during pregnancy, might affect the brain.
Krastel said she was not aware during the study of the data showing changes in her brain, and did not feel any different.
“Some people talk about ‘mommy brain’ and stuff like that,” she added, referring to the mental fog some pregnant women experience. “I’ve never really experienced any of that.”