Researchers have created one of the first comprehensive maps of how the brain changes throughout pregnancy, substantially improving upon understanding of an understudied field.
Certain brain regions may shrink in size during pregnancy yet improve in connectivity, 鈥渨ith only a few regions of the brain remaining untouched by the transition to motherhood,鈥� according to the study published Monday in the journal .
The findings are based on one healthy 38-year-old woman the authors studied from three weeks before conception to two years after her child鈥檚 birth. Dr. Elizabeth R. Chrastil, a professor at the University of California, Santa Barbara, underwent in vitro fertilization. Chrastil conceived the project and wished to use herself as the participant, as has been done in previous research.
There has been 鈥渟o much about the neurobiology of pregnancy that we don鈥檛 understand yet,鈥� said senior study author Dr. Emily Jacobs, associate professor in the department of psychological and brain sciences at UC Santa Barbara, in a news briefing on the study. 鈥淎nd it鈥檚 not because women are too complicated. 鈥� It鈥檚 a byproduct of the fact that the biomedical sciences have historically ignored women鈥檚 health. It鈥檚 2024, and this is the first glimpse we have at this fascinating neurobiological transition.鈥�
About 85 per cent of sexually active women who don鈥檛 use any birth control can expect to become pregnant within a year, and around 208 million women get pregnant every year.
鈥淭he brain is an endocrine organ, and sex hormones are potent neuromodulators, but a lot of that knowledge comes from animal studies,鈥� Jacobs said. Human studies tend to rely on brain imaging and endocrine assessments collected from groups of people at a single point in time.
鈥淏ut that kind of group averaging approach can鈥檛 tell us anything about how the brain is changing day to day or week to week as hormones ebb and flow,鈥� Jacobs added. 鈥淢y lab here at UC Santa Barbara uses precision imaging methods to understand how the brain responds to major neuroendocrine transitions like the circadian cycle, the menstrual cycle, menopause and now, in this paper, one of the largest neuroendocrine transitions that a human can experience 鈥� which is pregnancy.鈥�
How pregnancy transformed a mother鈥檚 brain
Jacobs and colleagues conducted 26 MRI scans and blood tests on the first-time mother, then compared them with brain changes observed in eight control participants who weren鈥檛 pregnant.
By the ninth week of pregnancy, the authors found widespread decreases in gray matter volume and thickness of the cerebral cortex, especially in regions such as the default mode network, which is associated with social cognitive functions. Gray matter is an essential brain tissue that controls sensations and functions such as speech, thinking and memory. After peaking during childhood, cortical thickness decreases throughout one鈥檚 lifespan.
The scans also showed increases in cerebrospinal fluid and white matter microstructure in the second and third trimesters, all of which were linked with rising levels of the hormones estradiol and progesterone. Cerebrospinal fluid helps provide nourishment, protection and waste removal for the brain. White matter helps areas of the brain communicate and process information.
Some of the changes 鈥� including cortical volume and thickness 鈥� remained two years after birth, whereas others reverted to levels similar to those of the preconception period by roughly two months postpartum. And compared with the control group, change in the woman鈥檚 gray matter volume was nearly three times higher.
鈥淭his study is fundamental in laying the groundwork for future research by providing data that allows future research to explore in more detail and look at in relation to how we can support healthy brain changes in pregnancy (in the mother which will likely impact that developing fetus),鈥� said Dr. Jodi Pawluski, a neuroscientist, therapist and author based in France, via email. Pawluski wasn鈥檛 involved in the research.
The case study also 鈥渟erves as a proof-of-concept that precision imaging studies are well-equipped to detect the full dynamic range of brain changes that unfold during the gestational period,鈥� said Dr. Magdalena Martínez García, a postdoctoral researcher in human neuroscience at the Jacobs Lab at UC Santa Barbara who wasn鈥檛 involved in the study.
What brain changes mean for parents
The functional implications these brain changes may have for birthing parents have yet to be determined, said Dr. Elseline Hoekzema, head of the Pregnancy and the Brain Lab at Amsterdam University Medical Center, via email. Hoekzema wasn鈥檛 involved in the study.
However, some of Hoekzema鈥檚 previous work has indicated associations between pregnancy-related brain changes and the ways a birthing parent鈥檚 brain and body respond and bond to infants鈥� cues, Hoekzema added. These findings are also in line with animal studies showing brain changes that were critical for the onset and continuation of maternal care.
The decreases in gray matter volume and cortical thickness could point toward an idea that for the maternal brain, 鈥渋t looks like less really may be more,鈥� Pawluski said. 鈥淚t鈥檚 potentially becoming more efficient.鈥�
The increase in white matter microstructure, on the other hand, could mean 鈥渁n increase in the exchange of information and communication between different brain areas,鈥� Pawluski said. The findings may also have important implications for preventing or treating perinatal mental health issues or supporting a healthy transition to motherhood.
Of course, these neural shifts occurring in one woman doesn鈥檛 mean they happen for all or to the same extent for everyone, so replication in studies with higher numbers of participants is needed, experts said.
However, research thus far shows the changes 鈥渁re relatively very consistent across different women,鈥� Hoekzema said. 鈥淚n one study we found that all the participants could be classified as having been pregnant or not by a computer algorithm based only on the changes in their brains. And so far we鈥檝e already replicated these changes.鈥�
Despite the unanswered questions, Pawluski said she wants birthing parents to know these changes are normal and healthy, rather than a deficit that some people believe is a stereotypical experience of motherhood.
鈥淥ur ignorance has consequences,鈥� Jacobs said. Scientists haven鈥檛 had the data, for example, to predict postpartum depression before it manifests or to understand the long-term effects of preeclampsia on brain health.
The study also represents the launch of the Maternal Brain Project, an international effort supported by the Ann S. Bowers Women鈥檚 Brain Health Initiative and the Chan Zuckerberg Initiative, for which a much larger cohort of women and their partners are being enrolled at UC Santa Barbara and in Spain.
鈥淲e need better data,鈥� Jacobs added. 鈥淥f the 50,000 brain imaging articles published in the last 30 years, less than half of one per cent focus on health factors unique to women, like pregnancy. So, when we talk about the scientific body of knowledge, we鈥檝e got to consider whose body does it serve.鈥�
