Their new study is the first to show that giving birth involves long-lasting changes—for at least two years afterward—in the structure of a woman’s brain. It's long been known that pregnancy causes hormonal and chemical surges throughout the body, but until now its impact on the brain has remained largely a mystery.
To investigate, scientists performed cognitive tests and magnetic resonance imaging (MRI) brain scans on 25 first-time mothers, both before they became pregnant and after they gave birth. The study also included 19 of their male partners, and a control group of 20 women (and 17 of their partners) who were not and had never been pregnant.
When the researchers compared before-and-after scans of the new moms, they noticed a reduction in gray matter in brain regions associated with social cognition, which involves the ability to perceive what others are thinking and feeling. This reduction was not seen in the new dads or the non-parents.
The authors believe that these changes happen for a very specific reason.
Co-lead author Elseline Hoekzema, PhD, currently a postdoctoral researcher at Leiden University in the Netherlands, said in a statement that this reduction in gray matter may reflect “synaptic pruning,” in which weak brain connections (or synapses) are eliminated to make room for more efficient, specialized networks.
This type of pruning also happens during adolescence, another time of major hormonal changes. In teenagers, it’s generally regarded as “an essential process of fine-tuning connections into functional networks,” the authors wrote, which is “critical for healthy cognitive, emotional, and social development.”
Co-author Oscar Vilarroya, MD, a neuroscientist at the Universitat Autònoma de Barcelona (UAB), said in a statement that the findings point to “an adaptive process related to the benefits of better detecting the needs of the child, such as identifying the newborn’s emotional state.”
For the new moms, further imaging tests showed that the brain regions where they lost gray matter overlapped with ones that “lit up” when the women watched images of their own babies. These changes were still visible in scans taken two years after they’d given birth, which was the final follow-up point in the study.
The changes were so distinct that brain scans alone were enough to reveal, with great reliability, whether a woman had been pregnant or not. They were even able to predict mothers’ level of attachment to their babies after they were born.
Thankfully, the loss of gray matter did not appear to be associated with any cognitive defects or changes in memory for the new moms. Rather, as co-lead author and UAB researcher Erika Barba-Müller said in the press release, “these changes concern brain areas associated with functions necessary to manage the challenges of motherhood.”