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HOW PREGNANCY CHANGES THE BRAIN  
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Gina Jiménez
March 15, 2024
Scientific American
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_ A study of more than 100 new parents showed that pregnancy and
birth cause changes in brain circuits that may be involved in empathy
and bonding with the child _

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Being pregnant and giving birth changes a person’s brain, but the
brain looks different depending on whether it’s examined during
pregnancy or after a person gives birth, a recent study
[[link removed]] found. The
research is helping disentangle some of the mysteries in the
long-ignored field of maternal neuroscience.

The study, published in January in _Nature Neuroscience,_ followed
more than 100 new mothers from near the end of their pregnancy until
about three weeks on average after they had their baby. Previous
research had examined birthing parents’ brain before they gave birth
or during the postpartum period, but this study observed them both
before and after birth, and it also took into account whether they had
a vaginal birth or C-section. The findings reveal temporary changes in
some brain regions and more permanent ones in a brain circuit that
activates when people are not engaged in an active task and that is
also involved in self-reflection and empathizing with others.

The study has “ordered” some of the scientific disagreements in
the field, says its senior author Susana Carmona, a neuroscience
researcher now at Gregorio Marañón General University Hospital in
Spain.*

“It fills important gaps—that is why it’s novel,” says Joe
Lonstein, a neuroscientist who studies animal parenting behaviors at
Michigan State University but was not involved with the new paper.
“There were things we just didn’t know about the timing of
events.”

Much of the scientific literature on pregnancy and postpartum
neuroscience is only around a decade old. A 2016 study found
that gray matter decreased
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baby for the first time, and the reductions persisted for at least
six years
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pregnancy. In contrast, other studies have observed that gray
matter _increases_ in the first weeks after people give birth. The
new paper helps reconcile these results: the researchers found that
women indeed lost gray matter during pregnancy and childbirth but got
it back in most brain areas after they had their baby.

Previous studies have mainly observed changes in specific brain areas
involved in a circuit called the default mode network. This network
activates when a person’s mind is wandering or when they are not
doing a specific task, but researchers have also found it is key to
self-reflection and to the creation of an “internal narrative,”
which is central to the construction of a “sense of self” and to
how we interact with others. Several
[[link removed]]studies
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linked this network activation to people’s capacity to empathize
with others, and researchers believe the changes that occur during
pregnancy or birth could help parents empathize with their babies. A
study in 2016 [[link removed]] linked the
pregnancy gray-matter reductions in this network to an increase in
brain activity when women were shown photographs of their baby crying
and better parent-child attachment. Researchers also think some of the
brain changes pregnant people undergo might prepare them not only for
parenthood but for childbirth itself—by increasing pain tolerance,
for example.

Carmona’s study focused on the default mode network and other brain
circuits and found that the former is the only circuit that doesn’t
fully go back to its prepregnancy state—and the change persists for
many years after people give birth.

Researchers believe that the changes that happen to birthing parents
during pregnancy and after birth is similar to those that affect
everybody in their teenage years. Teenagers also experience a gray
matter reduction because many brain connections, or synapses,
disappear during that phase in a process known as “synaptic
pruning.” That is not a bad thing. If you are trying to get
somewhere on a highway with many, many paths, you are likely to get
lost, Carmona says. The brain simply eliminates some of those
“paths” to streamline information processing.

Just as Michelangelo’s _David_ was sculpted from a block of
marble, “the beauty is revealed by removing the excess,” says
Emily Jacobs, a neuroscientist at the University of California, Santa
Barbara, who studies how sex hormones change the brain and was not
involved in the new paper.

And there is something else pregnant people and teenagers have in
common: huge hormonal changes. Researchers hypothesize that the
hormonal roller coaster that comes with childbearing is responsible
for these brain changes. In animal studies, scientists gave pregnancy
hormones [[link removed]] to mice
and observed brain changes associated with maternal behavior, Lonstein
says. Of course, mice are not humans, and there haven’t been many
experiments testing this hypothesis in people.

The new study also found that women who had a vaginal birth or started
going into labor but ultimately had an emergency cesarian section took
longer to “recover” from the gray matter declines than women who
had a scheduled C-section. “Going into labor triggers its own
hormonal and immune cascade,” Carmona says. The researchers had a
small sample size for this part of the study, however, so they say the
findings should be interpreted with caution.

One challenge of doing this type of research is finding people who are
willing to participate. “It’s really, really hard to find women
who are willing to do these things at a time in their life that can be
both joyous but also very stressful,” Lonstein says.

The study has opened up a series of questions, such as “Do
nonbirthing or adoptive parents undergo similar brain changes?” and
“What is the effect of labor on the birthing parent-child bond?”
Only about 0.5 percent
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studies look at topics exclusive to women’s health, according to an
article by Jacobs, and there is still a lot we don’t know about how
pregnancy changes the brain.

Jacobs thinks the fact that there have historically been few women in
neuroscience may partially explain why so many of these questions
weren’t addressed before. “These are women asking these questions.
So it makes a pretty strong case for why diversity in science
matters,” she says.

_GINA JIMÉNEZ
[[link removed]] is a
bilingual journalist focused on health and science policy and how they
affect disadvantaged communities. Follow her on X (formerly
Twitter) @GinaRivers90 [[link removed]]_

_More by Gina Jiménez
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_Discover something new everyday with a subscription to Scientific
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* Science
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* biology
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* neuroscience
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* pregnancy
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* mothers
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