A recent study has revealed how pregnancy dramatically alters brain structure, with more than 80% of the brain’s gray matter shrinking during pregnancy and leaving lasting imprints even after childbirth. The study, which focused on detailed brain scans collected before, during, and after one neuroscientist’s pregnancy, shows that although some of this gray matter returns postpartum, much of it remains permanently reduced.
Gray matter is a critical part of the brain that consists of neuronal cell bodies and their connections, playing a significant role in processing information. The study found that, on average, there was a 4% reduction in gray-matter volume in the affected brain regions. Emily Jacobs, an associate professor of psychological and brain sciences at the University of California, Santa Barbara (UCSB), and co-senior author of the study, noted that these changes in brain structure are comparable to those seen during puberty, another period of significant hormonal change. During puberty, the brain undergoes a process known as “pruning,” where excess tissue is removed to optimize its efficiency, and something similar seems to occur during pregnancy.
“Sometimes people react with concern when they hear that gray matter decreases during pregnancy, thinking it must be negative,” Jacobs said. However, she emphasized that these reductions likely reflect a fine-tuning of neural circuits, much like the cortical thinning observed during adolescence. This refinement may have long-term implications, with Jacobs referring to these changes as “permanent etchings” in the brain.
In addition to the changes in gray matter, the study also observed that white matter, which consists of the brain’s “wiring” that connects neurons, became more robust during the first two trimesters. White matter allows information to flow efficiently between different regions of the brain. Liz Chrastil, an associate professor of neurobiology and behavior at the University of California, Irvine, and the study’s other senior co-author, explained that when white matter is strong, information can be transmitted with less resistance, much like water flowing smoothly through a tube. However, by the time of birth, the scans revealed that the white matter had returned to its pre-pregnancy baseline, resetting after this temporary enhancement.
Remarkably, Chrastil revealed that she was the participant in the study, having undergone more than two dozen brain scans throughout her pregnancy and for two years postpartum. The research team collected four MRI scans prior to conception, 15 during pregnancy, and seven after the birth of her child. Chrastil admitted that she had no idea how her brain was changing until after all the data had been gathered and analyzed, calling the entire process an “intense undertaking.”
Although Chrastil did not experience “mommy brain”—a term used to describe cognitive lapses during pregnancy and after childbirth—or any complications such as preeclampsia, her brain scans now serve as a “baseline” to compare against pregnancies with complications. Preeclampsia, a condition that affects the brain’s blood vessels, can increase the risk of stroke and vascular dementia. Understanding how pregnancy affects the brain in more typical cases like Chrastil’s could shed light on how these changes might differ in complicated pregnancies. Additionally, some conditions like migraines and multiple sclerosis tend to improve during pregnancy, though the reasons for these improvements are still unclear. Detailed brain maps, like those produced in this study, may help explain the underlying mechanisms behind these changes.
While this study focused on a single individual, the results align with findings from larger studies that tracked first-time mothers over time. According to Magdalena Martínez-García, a postdoctoral researcher in human neuroscience at UCSB, these brain changes appear to be common in pregnant women, suggesting that the phenomenon may be widespread. Other experts, such as Elseline Hoekzema, a neuroscientist studying pregnancy’s effects on the brain at Amsterdam University Medical Center, agree that the results likely reflect broader patterns, even though the study involved only one participant.
Despite these intriguing findings, this is only the beginning. Chrastil and her collaborators have launched the *Maternal Brain Project*, a global initiative aimed at collecting brain scans from a larger number of pregnant individuals. Early data from participants who have already completed their scans show similar patterns of brain changes, and researchers hope that expanding the study will provide even deeper insights into how pregnancy shapes the brain.
As this research progresses, it promises to enhance our understanding of not only how pregnancy alters the brain but also how these changes might influence cognition, behavior, and disease susceptibility in new mothers.
