Researchers have created one of the first comprehensive maps of how the brain changes during pregnancy, significantly expanding their knowledge of a previously understudied field.
Certain brain regions may become smaller during pregnancy yet remain better connected, "with only a few brain regions remaining unaffected by the transition to motherhood," according to the study published Monday in the journal Nature Neuroscience.
The findings are based on a healthy 38-year-old woman whom the authors studied from three weeks before conception to two years after the birth of her child. Dr. Elizabeth R. Chrastil, a professor at the University of California, Santa Barbara, underwent in vitro fertilization. Chrastil conceived the project and wanted to use herself as a participant, as has been done in previous research.
"There's so much about the neurobiology of pregnancy that we don't understand yet," lead study author Dr. Emily Jacobs, an associate professor in the department of psychology and brain sciences at UC Santa Barbara, said in a press briefing about the study. "And it's not because women are complicated. ... It's a byproduct of the fact that the biomedical sciences have historically ignored women's health. It's 2024, and this is the first glimpse we're getting into this fascinating neurobiological transition."
READ MORE: Why You're Not a Failure as a Mother
About 85% of sexually active women who do not use contraception can expect to become pregnant within a year. About 208 million women become pregnant each year.
"The brain is an endocrine organ, and sex hormones are powerful neuromodulators, but much of that knowledge comes from animal studies," Jacobs said. Human studies typically rely on brain imaging and endocrine assessments collected from groups of people at one point in time.
"But that kind of group-average approach can't tell us anything about how the brain changes from day to day or week to week as hormones ebb and flow," Jacobs added. "My 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 biggest neuroendocrine transitions a human can experience - pregnancy."
How Pregnancy Transformed a Mother's Brain
Jacobs and colleagues performed 26 MRI scans and blood tests on the first-time mothers and then compared them to brain changes observed in eight control participants who were not pregnant.
By the ninth week of pregnancy, the authors found widespread decreases in the volume and thickness of gray matter in the cerebral cortex, particularly in regions such as the default mode network, which is associated with social-cognitive functions. Gray matter is a critical brain tissue that controls sensations and functions such as speech, thinking and memory. After peaking in childhood, cortical thickness decreases throughout a person's life.
The scans also showed increases in cerebrospinal fluid and white matter microstructure in the second and third trimesters, all of which were linked to rising levels of the hormones estradiol and progesterone. Cerebrospinal fluid helps nourish, protect and remove waste from the brain. White matter helps areas of the brain communicate and process information.
Some changes - including cortical volume and thickness - persisted two years after birth, while others returned to levels similar to those seen before conception, about two months after delivery. And compared with controls, the women's gray matter volume changed nearly three times as much.
"This study is fundamental in laying the foundation for future research by providing data that will allow future research to examine in more detail and look at how we can support healthy brain changes during pregnancy (in the mother that will likely impact the developing fetus)," said Dr. Jodi Pawluski, a neuroscientist, therapist and author based in France, via email. Pawluski was not involved in the study.
The case study also serves as "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," said Dr. Magdalena Martínez García, a postdoctoral researcher in human neuroscience in the Jacobs Lab at UC Santa Barbara who was not involved in the study.
What Brain Changes Mean for Parents
The functional implications these brain changes may have for parents giving birth remain to be determined, said Dr. Elseline Hoekzema, head of the Pregnancy and the Brain Lab at Amsterdam University Medical Center, via email. Hoekzema was not involved in the study.
However, some of Hoekzema's previous work has shown associations between pregnancy-related brain changes and the ways a birthing parent's brain and body respond to and engage with baby's cues, Hoekzema added. These findings also align with animal studies showing brain changes that were crucial for the initiation and continuation of maternal care.
The decrease in gray matter volume and cortical thickness could point to a notion that for the mother brain, "it seems like less really can be more," Pawluski said. "It might become more efficient."
The increase in white matter microstructure, on the other hand, could mean "an increase in the exchange of information and communication between different brain regions," Pawluski said. The findings could also have important implications for preventing or treating perinatal mental health problems or supporting a healthy transition to motherhood.
However, just because these neural shifts occur in one woman doesn't mean they occur in all women or to the same extent in everyone. That's why the results need to be replicated in studies with a larger number of participants, experts say.
Research to date, however, shows that the changes are "relatively very consistent across women," Hoekzema said. "In one study, we found that all participants could be classified as pregnant or not by a computer algorithm based solely on the changes in their brains. And so far, we've replicated those changes."
Despite the unanswered questions, Pawluski wants parents who are having a child to know that these changes are normal and healthy, and not a deficiency that some people see as a stereotypical experience of motherhood.
"Our ignorance has consequences," Jacobs said. For example, scientists don't have the data to predict postpartum depression before it occurs or to understand the long-term effects of preeclampsia on brain health.
The research also marks the launch of the Maternal Brain Project, an international initiative supported by the Ann S. Bowers Women's Brain Health Initiative and the Chan Zuckerberg Initiative, which includes a much larger group of women and their partners at UC Santa Barbara and in Spain.
"We need better data," Jacobs added. "Of the 50,000 brain imaging papers published in the last 30 years, less than half of 1 percent focus on health factors unique to women, like pregnancy. So when we talk about the science, we have to consider whose body it serves."
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