What exactly is a pregnancy brain? We may finally have some answers.

“Pregnancy is like a stress test for the body," says Emily Jacobs, director of University of California, Santa Barbara’s Ann S. Bowers Women’s Brain Health Initiative, and a co-author on study. 

The massive changes include shifts in hormone levels and the immune system, and more work for organs like the heart and kidneys. Yet, to date little has been known about the details of brain changes. Jacobs points out that less than 0.5% of the 50,000 brain imaging studies published since the 1990s specifically focus on women’s health.

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The previous studies we have, while early steps in this field of maternal brain mapping, only captured images of the brain before and after childbirth (with one recent large study also getting a third trimester peek). 

The UC researchers went far further. MRIs were conducted before conception, every few weeks during gestation, and two years after birth for a total of 26 scans—offering a more comprehensive picture of the brain’s transformation during and after pregnancy.

“This approach captures subtle neural variations that might otherwise go unnoticed, enhancing our comprehension of brain adaptations during this critical period," Ann-Marie de Lange, head of FemiLab at Lausanne University Hospital in Switzerland, said in an email.

Indeed, researchers found what prior research would have missed: a metamorphosis driven by hormonal fluctuations, with some changes in the brain returning to baseline by birth and others persisting for years after. 

Most strikingly, nearly all parts of the cortex showed a reduction in grey matter, the tissue responsible for processing and interpreting information, commandeering things like movement and memory. It persisted for years after birth.

That might sound alarming. The part of the brain responsible for processing is… shrinking? Jacobs compares the transformation to Michelangelo sitting before a block of marble. “The underlying beauty is revealed through the art of removal, carefully honing and fine tuning the material." 

In other words, this amazing display of neuroplasticity could potentially represent not a loss of function, but a gain in efficiency as women prepare for parenthood. It’s an exercise in cortical refinement that the brain undertakes at a few distinct stages of a woman’s life—adolescence, matrescence and again during menopause.

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They also found transient increases in the quality of connections in the brain tissue known as white matter, peaking in the second and third trimester before returning to baseline at birth. We’ll need more research to tell us what this metamorphosis means for human behaviour. 

Animal scans have linked certain brain changes to a mother’s sensitivity to smells and sounds from her newborns and maternal behaviour like nest building and grooming.

“Humans are way more complicated," Jacobs says, and parental behaviour manifests in partners, grandparents, adoptive parents and others. The UC team has already captured biweekly snapshots of the brains of seven more pregnant women and plans to recruit up to 20 people. 

Eventually, more than 200 first-time mothers will be followed monthly. The hope is to illuminate changes in the brain during pregnancy across women from many walks of life to help scientists better understand the underlying mechanisms of and risks for conditions like preeclampsia, migraines and postpartum depression. 

Researchers will need to look not only at the anatomical changes in the brain, but study the vascular and functional ones, says Joana Pinto, a neuroimaging expert who leads Oxford’s Maternal Brian Project.

Preeclampsia is a dangerous condition typically marked by soaring blood pressure. All pregnant women experience increased blood flow to the brain during pregnancy, but something goes awry in women with preeclampsia, explains Pinto.

Women’s health has been understudied for far too long. “Thankfully, there’s growing understanding that these fluctuations play a dynamic role in brain structure and function, and that findings based on male participants do not necessarily apply to women—we are not just smaller versions of men," says de Lange.

Also read: Becoming a father shrinks your cerebrum

Studies like this one are critical to closing the egregious knowledge gap in the field of neurobiology—and in medicine overall. ©bloomberg