Pregnancy causes dramatic changes in the brain, study confirms

A new study used functional magnetic resonance imaging to show dramatic changes in the brain during pregnancy. Pregnancy increased gray matter loss and reshaped the default mode network, which is responsible for the mind wandering and a sense of identity. (Image credit: National Institute of Mental Health, National Institutes of Health)

Pregnancy leads to striking changes in the brain, including alterations in gray matter and regions involved in self-perception, according to a new study.

"These data provide key insights into the impact of becoming a mother on the human brain and point to pronounced changes in brain structure and function" during pregnancy, the authors wrote in the study, which was published Nov. 22 in the journal Nature Communications.

These changes "may confer adaptive advantages for a mother's gestational and maternal behavior and the establishment of the new mother-child relationship," according to the study researchers, from Amsterdam University Medical Center.

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In an earlier study of pregnant women in Spain, the same group of researchers found that the participants had a reductions in the amount of gray matter in their brains and that these reductions lasted up to two years after the women gave birth. In the new study, conducted in the Netherlands, the researchers expanded on this work by examining more brain areas and investigating whether the changes were linked with certain behaviors and measures of the mother-infant bond.

They followed 80 Dutch women who were not pregnant at the start of the study and had never had a baby before. Over the course of the study, 40 of the women became pregnant. All of the women had their brains scanned at the start of the study and at various points afterward, including (for those who became pregnant) shortly after giving birth and one-year postpartum.

The researchers again found that the women who became pregnant lost gray matter after giving birth. Replicating the finding in their previous study further suggests that these results are reliable and are seen in people in different countries, the authors said. These gray matter losses aren't necessarily detrimental; rather, they may represent a "fine-tuning" of the brain that could be beneficial in caring for a new baby, they said.

Interestingly, losing gray matter was linked with so-called nesting behaviors, which are carried out to get ready for the arrival of the baby — for example, preparing the nursery or organizing the house.

The study also found that the women who became pregnant showed changes in a brain system known as the default mode network, a group of brain regions that are most active when a person isn't doing a specific task. This network is active when you let your mind wander and is thought to be involved in self-reflection and autobiographical memory, as well as in social processes such as empathy, the authors said.

What's more, women with bigger changes in the default mode network reported feeling a greater bond with their infant (as measured by a survey of mother-infant bonding) and taking more pleasure in interacting with their infant compared with women with smaller changes. Women with bigger default-mode-network changes also reported fewer "bonding impairments," such as feelings of resentment or anger toward the baby. In addition, the brain changes were linked with measures of attachment to the fetus — specifically, the greater the increases in activity in the default mode network were, the more likely women were to differentiate the fetus from themselves and see the fetus as an individual.

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The researchers speculated that changes to the default mode network in pregnancy may alter the neural basis of the self, "contributing to the transformation in a woman's identity and focus that often accompany new motherhood," the authors said.

Finally, the researchers investigated what factors could be driving these brain changes, and their results point to a likely culprit: hormones. Using urine samples collected at 10 points during the study, the researchers found that women with higher levels of estrogen, particularly during the third trimester of pregnancy, showed greater brain changes than those without such a pronounced spike in estrogen. In contrast, factors such as sleep, stress levels and the type of delivery weren't linked with the brain changes.

Still, the researchers can't rule out the possibility that other factors not measured in the study — including exercise, nutrition and genetic markers — could be involved in these brain changes, and they called for further, larger studies to examine these factors.

Rachael has been with Live Science since 2010. She has a masters degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a Bachelor of Science in molecular biology and a Master of Science in biology from the University of California, San Diego.