During pregnancy, a woman’s body undergoes a variety of changes – hormonal, cardiovascular, respiratory, digestive, urinary and more. But what changes occur in the brain has not been well studied in humans.

New research published in Nature Neuroscience has shown that significant changes also occur in the brain, some of which are temporary, while others are long-lasting.

For the first time, researchers have mapped these brain changes by scanning the brain 26 times, starting three weeks before conception, through nine months of pregnancy and continuing for two years after birth.

The study found that the outer layer of the brain, called gray matter, decreased in size, while the deeper white matter, which helps different parts of the brain communicate, became more structured.

These changes were caused by increased levels of the pregnancy hormones, estradiol and progesterone.

Gray matter contains the cell bodies of the brain’s nerve cells, while white matter contains long fibers that transmit signals in the brain.

The study focused on just one subject: Elizabeth Crostill, a neuroscientist and co-author of the study.

She was 38 years old when she participated and gave birth to a healthy boy, who is now four and a half years old.

Since then, scientists have observed the same pattern in other pregnant women as part of ongoing research called the Maternal Brain Project, which aims to expand the study to hundreds of women.

“It’s astonishing that even in 2024, we still know so little about how pregnancy affects the brain,” Krastill said. “This study raises more questions than it answers, and we’re just beginning to explore them.”

The scans showed that, on average, gray matter volume declined by about 4% in 80% of the brain regions studied. There was a slight recovery after birth, but it did not return to pre-pregnancy levels.

On the other hand, white matter structure showed a 10% improvement, peaking in the late second and early third trimesters, and returning to pre-pregnancy levels after birth.

Previous research only compared brain scans before and after pregnancy, but this is the first time scientists have been able to look at changes in the brain during pregnancy.

It is still unclear whether a reduction in gray matter is harmful.

“It may be that the brain is repairing itself, just as it does during puberty when the brain becomes more specialized,” said study lead author Laura Pritchett. “Some of these changes may also be a response to the physical demands of pregnancy, showing how adaptable the brain can be.”

Crostill, who didn’t feel any different during the study, reflected on the experience, saying: “It’s interesting to look back now and think, ‘That was an exciting trip.'”

She also reported that she didn’t experience “mommy brain,” as some women describe it in reference to the mental fog they experience during pregnancy.