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 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.*
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“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 in women after they had a baby for the first time, and the reductions persisted for at least six years after 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. Severalstudies have 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 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 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 of neuroscience 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.
*Editor’s Note (11/18/24): This sentence was edited after posting to correct Susana Carmona’s affiliation.