Pregnancy is associated with extensive physiological changes, including hormonal, cardiovascular, respiratory, gastrointestinal, urinary alterations, and more. A new study indicated that the brain also undergoes significant changes during this period, with some being transient and others more persistent.
Researchers have mapped, for the first time, the changes occurring in a woman's brain in response to pregnancy. This mapping was based on 26 brain scans conducted from three weeks before conception, throughout the nine months of pregnancy, and up to two years postpartum.
The study documented a substantial decrease in the volume of cortical gray matter, which is the outermost layer of the brain, and an increase in the microstructural integrity of white matter located deeper in the brain. Both changes were observed alongside rising levels of estradiol and progesterone.
Gray matter consists of the cell bodies of nerve cells, while white matter comprises bundles of axons—long fibers that transmit signals across the brain.
The study, published in Nature Neuroscience, was initially based on a single participant, Elizabeth Chrastil, PhD, a cognitive neuroscientist at the University of California, Irvine, who participated as a first-time mother.
Since the study’s completion, researchers have observed similar patterns in several other pregnant women in an ongoing research initiative known as the Maternal Brain Project, with plans to expand the sample size to hundreds of participants.
"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," said Chrastil.
The scans revealed an average reduction of about 4% in gray matter in approximately 80% of the regions studied. Although there was a slight rebound postpartum, the volume did not return to pre-pregnancy levels. Additionally, an increase of about 10% in white matter microstructural integrity, a measure of the health and quality of brain region connections, was observed, peaking late in the second trimester and early in the third trimester before 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," stated Emily Jacobs, PhD, a neuroscientist at the University of California, Santa Barbara, and senior author of the study.
"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 indicated that the loss of gray matter might not necessarily be detrimental.
"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 specialized. 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," said Laura Pritschet, a postdoctoral scholar at the University of Pennsylvania and the study's lead author.
The researchers hope in the future to explore how variations in these brain changes might predict phenomena such as postpartum depression or the effects of conditions like preeclampsia.
Chrastil noted that she was not aware of the changes in her brain during the study and did not feel different.
"And so, you know, now there's some distance to be able to say, 'OK, well, that was a wild ride,'" she remarked.
"Some people talk about 'Mommy Brain' and things like that," Chrastil added, referencing the mental fogginess some pregnant women report. "And I didn't really experience any of that."
