Researchers said Monday they have for the first time been able to map the changes that occur as the brain reorganizes itself in response to pregnancy, based on 26 scans over a broad period from three weeks before conception through nine months of pregnancy and up to two years after birth.
The study documented a widespread reduction in the volume of gray matter known as the cerebral cortex, a wrinkled shell that forms the outer layer of the brain, as well as an increase in the fine structural integrity of the brain’s inner white matter.
The changes coincided with increased levels of the hormones estradiol and progesterone.
Grey matter consists of the cell bodies of neurons in the brain, while white matter consists of bundles of axons (long, thin fibers) of neurons that transmit signals over 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 four-and-a-half-year-old boy. She was 38 when she was studied, and is now 43.
Since completing the study, the authors said, they have observed 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.
The study’s authors aim to increase the number of cases covered by the project to hundreds.
“It’s shocking that in 2024 we still 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.”
According to Krastel, she was not aware of the data showing changes in her brain during the study, and she did not feel any difference.
“Some people talk about mommy brain and stuff like that, but I’ve never really experienced any of that,” she added, referring to the mental fog some pregnant women experience.
Study results
The scans showed an average four percent shrinkage of gray matter in about 80 percent of the brain regions studied.
Mild postpartum rebound did not result in a return of cortical volume to pre-pregnancy levels.
The tests 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 and 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 in the midst of this transformation,” she added.
According to the researchers, it is not clear whether the loss of gray matter is a bad thing.
“This change could be 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 the University of Pennsylvania 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 serious condition of high blood pressure that can develop during pregnancy, might affect the brain.
