Women actually lose part of their brain during pregnancy — but there’s a bright side

Is she “crazy,” or is her gray matter just being compressed?

Neuroscientists in Spain have found a connection between pregnancy hormones and fluctuating gray matter in the brain — which could help illuminate more about the postpartum period and attachments between mothers and newborns.

A study done in association with the BeMother project found that pregnancy likely leads to a temporary dip in gray matter.

This might otherwise be cause for concern, but in this case, the eventual rebound of that gray matter seems to heavily impact the mental health of new moms — and actually help them form postpartum bonds with their babies.

Gray matter, the brain and spinal cord tissue that assists in processing sensory information and decision-making, potentially gets compressed during pregnancy by the increasing fluid flowing to the brain. 

On average, the pregnant women involved in the study lost nearly 5% of their gray matter, affecting large swaths of the brain, including regions that dictate social cognition.

Susana Carmona, a professor at the Gregorio Marañón Health Research Institute in Madrid and co-leader of the study, described this decrease in tissue in botanical terms. “I like to use the metaphor of pruning a tree. Some of the branches are cut to make it grow more efficiently,” she said.

And while some of the gray matter is renewed in the postpartum phase — a process that we can now associate with healthier mother-baby bonds — this study also indicates that the gray matter never fully rebounds to its pre-pregnancy levels.

The authors characterize this experience in first-time mothers as a “remodeling of brain architecture,” brought on by gestational hormones. In particular they examined two types of estrogens, estriol and estrone sulfate, which “surge” during pregnancy to produce placenta, and then “plummet” after the placenta is expelled during childbirth.

In addition to external environmental factors, the new brains engineered by those hormones have an outsized influence on mother-baby relationships.

This study found that a higher percentage of postpartum gray matter recovery led to less “hostility towards the infant at 6 months postpartum,” suggesting that the “brain remodeling experienced by gestational mothers might be adaptive, facilitating facets of maternal behavior.”

This may help partially explain why pregnancy and postpartum are considered “high risk” stages for mental health disorders. The World Health Organization estimates that 10% of pregnant women and 13% of postpartum women worldwide experience a mental health disorder, especially depression.

There are, in some cases, plenty of social explanations for poor maternal mental health, which could be driven by anything from lack of supportive parental leave policies from employers, substandard maternal health care, chronic stress and health care inequities tied to race, and other factors.

But this study confirms that biology does also play an unmistakable role.

The researchers used MRIs and urine samples to analyze the brains and hormone levels of 179 women before, during and after pregnancy. To underscore the differences between becoming a mother and physically undergoing a pregnancy, the researchers included several queer female couples in their study. 

Findings from those couples — which included one pregnant partner and one non-gestational partner, both preparing for motherhood — allowed the researchers to conclude that neurological changes are the outcome of “the biological process of pregnancy, rather than the experience of becoming a mother,” according to a press release from the Universitat Autonoma de Barcelona. 

The researchers are calling for future studies to incorporate “precise assessments of childrearing involvement and parent-infant interactions to further understand the functional meaning of these brain changes.”

But for now, this work gives us vital clues about how to better care for expectant and new mothers. 

“Together, these findings open the door to identifying specific periods during pregnancy and postpartum when experiences and interventions may have the greatest impact on maternal brain health and psychological well-being,” the authors wrote.