How Pregnancy Changes the Brain
Throughout pregnancy, a person’s body goes through many changes to eventually bring a child into the world. Metabolic rate—how much energy a body needs just to function—and oxygen consumption can increase. Hormones surge, and the immune system changes.
But what happens to the brain?
Research with rodents suggests that hormonal surges during pregnancy rewire the brain, coinciding with increased nesting and grooming behaviors. In these animals, the volume of gray matter, which is composed of neuronal cell bodies, changes temporarily in some brain regions.
Of course, humans are not rodents, and the human body may respond differently when pregnant. Researchers only began to systematically study pregnancy’s effects on the human brain within the past decade.
A Dearth of Data
“There’s so much about the neurobiology of pregnancy we don’t understand yet,” said Emily Jacobs, PhD, associate professor of psychological and brain sciences at the University of California, Santa Barbara and director of the Ann S. Bowers Women’s Brain Health Initiative. “It’s not because women are too complicated or because pregnancy is the Gordian knot of biology. It’s a byproduct of the fact that the biomedical sciences often overlook health factors specific to women—like pregnancy.”
“There’s so much about the neurobiology of pregnancy we don’t understand yet.”
Even as more researchers have become mindful of including women in clinical trials, studies still are not widely addressing women’s health topics. Dr. Jacobs pointed out that only 0.5% of the approximately 50,000 neuroimaging articles published in scientific journals since 1995 have considered issues specific to women.
Safety has also been a concern. Researchers have been hesitant to expose pregnant humans and fetuses to the high magnetic fields of magnetic resonance imaging (MRI) machines.
“For a long time, pregnant people generally were not studied by researchers using MRI, except in cases of medical need,” said Kathryn Humphreys, PhD, EdM, associate professor of psychology and human development at Vanderbilt University in Nashville, Tennessee. So, before Dr. Humphreys conducted MRI studies with pregnant participants, she consulted with many experts, such as ob-gyns, imaging scientists and bioethicists, who ultimately gave her the green light. (Several studies in the past decade have showed MRI to be safe during pregnancy, including in the first trimester.)
The topic is also logistically difficult to study. Because longitudinal research—examining the same person over a longer period of time—gives uniquely valuable information, this approach is ideal but prolonged.
“You want to investigate women before they get pregnant; then you have to wait until they become pregnant, give birth and so on,” said Elseline Hoekzema, PhD, head of the Pregnancy and Brain Lab at the Amsterdam University Medical Center in the Netherlands. “These studies take forever.”
Before and After
Early human imaging studies often included a small number of participants or only compared data from limited time points, such as before and after pregnancy. Although the overall picture was still a bit blurry, the earliest evidence suggested that pregnancy changes the human brain.
One of the first MRI studies on pregnant participants was published in 2016 by Dr. Hoekzema. First-time mothers had reductions in gray matter volume—particularly in regions involved in social interactions—after giving birth, compared to before becoming pregnant. Variations in these brain areas correlated with increased maternal attachment (as assessed by surveys). They also correlated with brain regions that became active in functional MRI scans when women were shown photos of their babies. In addition, the structural changes were so distinctive that a computer program could distinguish which participants had been pregnant based solely on these data. Brain changes persisted for up to two years.
A decrease in gray matter may sound alarm bells and make people think of “baby brain,” the catch-all phrase used to explain occasional forgetfulness during pregnancy. However, experts are quick to explain that less is more in this case.
This process, called synaptic pruning, is the brain’s way of making more precise and efficient connections, Dr. Jacobs explained. This is a natural and critically important process in which the brain prunes away unnecessary connections in the cortex to streamline its functions.
A 2019 study found that the brains of middle-aged women who had given birth to children were different, even decades later.
The findings related to pregnancy are reminiscent of another major hormonal life transition—adolescence—in which similar reductions occur. “We know from studies on adolescence that there’s actually pathologies that happen when the brain does not prune away connections or show that reduction in gray matter volume,” she said. For example, schizophrenia is a disorder that can result from too much pruning in the teen or early adult years.
Further evidence of pregnancy’s long-lasting effects came from a 2019 study that found that the brains of middle-aged women who had given birth to children were different, even decades later, compared to those who did not give birth. Women who had given birth also had brains that were biologically younger.
Other research showed that these changes were specific to the physiological experience of pregnancy and correlated with surges in estrogen. When the brains of pregnant women and mothers were compared to the brains of other parents who had not experienced pregnancy directly, the differences were clear. “Researchers have looked at fathers’ brains and the brains of non-birthing mothers [and] lesbian couples, and they have found that those brains don’t really change much, so it’s definitely the pregnancy—it’s not the experience of parenting,” said Sarah McKay, PhD, author of the book “Baby Brain.”
The Missing Piece
Recent studies have started to fill in the knowledge gap, showing what happens to the human brain during pregnancy. The new research confirms the earlier findings of a reduction in gray matter volume, but it picks up on some new nuances.
Dr. Jacobs led an MRI-based study in which the team scanned one pregnant woman every two weeks before, during and after pregnancy. “Nobody had really looked at pregnancy itself to understand the time course of these changes from different tissues in the brain,” Dr. Jacobs said. “It turns out it’s changing in pretty profound ways.”
Their research produced the first map of the brain across pregnancy, showing waves of remodeling throughout gestation. Gray matter volume and cortical thickness decreased from pre- to post-pregnancy, as others had observed, likely due to the process of pruning. There was also a gradual increase toward, but not reaching, pre-pregnancy levels. These changes lasted up to two years.
The white matter of the brain—made of axons, which are long wire-like fibers that help neurons communicate with each other—may react differently than the gray matter. In Dr. Jacobs’ study, the strength of white matter pathways was enhanced during certain parts of pregnancy, including the first and second trimesters, then returned to baseline levels by the end of pregnancy.
The behavioral changes associated with these findings have not been determined yet. However, researchers suspect that these changes may strengthen areas of the brain critical to parenthood, such as areas that support relational bonding and social cognition—or how we understand social situations and the behavior of others.
In a 2025 pilot study of 10 pregnant women, Dr. Humphreys reported similar results, including a hint that white matter may become more dense. Another team scanned 127 women before, during and after their first pregnancy and saw a decrease in white matter volume during pregnancy. Dr. Jacobs explains more research is needed to determine whether these are real differences or just different ways of seeing the same phenomenon.
What Does It All Mean?
Because this research area is so new, scientists are still trying to determine how all of these data fit together. “We’ve only recently discovered [that] these massive changes occur and are now in the stage of trying to figure out more about their functional implications for the mother and baby,” Dr. Hoekzema said.
Some researchers think these brain changes may help prepare women for motherhood. Research has shown potential connections between these brain changes and the mother-baby bond as well as a relationship between the quality and nature of these brain changes and vulnerability to conditions like postpartum depression and postpartum psychosis.
“If you are pregnant and you feel you have changed, know that you have changed … so cut yourself a break and be a bit kinder to yourself.”
However, experts express caution about assuming that these brain changes contribute directly to motherhood-related behavioral and mood changes. Much of this research is still based in correlation—correlation means the factors may be connected but it doesn’t necessarily mean that one factor caused the other. Further research is needed to determine whether the structural changes actually caused the differences in behavior. Furthermore, many people who do not experience pregnancy successfully parent children without undergoing these brain changes.
“It takes a tremendous amount of work to grow an entire human being, and all of the changes that are happening to support fetal growth and to prepare the body for delivery are likely to have some consequences for the person who’s pregnant,” Dr. Humphreys said. “But that doesn’t mean it’s necessarily by design to help them in their caregiving role.”
The work also opens up many new questions. Researchers are now beginning to investigate how these variations relate to pregnancy complications, such as preeclampsia and postpartum depression.
In the end, Dr. McKay said there is comfort in knowing more about this neurobiological transition. “If you are pregnant and you feel you have changed, know that you have changed—it’s not just social or psychological; it’s literally a neurological change,” she said. “So, cut yourself a break and be a bit kinder to yourself.”
