Pregnancy overhauls the brain. Here’s what that looks like

Pregnancy overhauls a woman’s body. The brain is no exception.

A detailed study of a woman’s brain before, during and after pregnancy revealed sweeping neural changes, some of which stuck around months after her baby was born. The dataset, published September 16 in Nature Neuroscience, is the first comprehensive view of the neural changes that accompany gestation — a sort of “what to expect when you’re expecting” for the brain.

“The results of this case study are astonishing,” says neuroscientist Clare McCormack of New York University Langone Health. “Here we see, for the first time in humans, the extent of brain changes that are under way throughout pregnancy.”

This research joins a small number of other studies aimed at understanding the female brain at various stages of life (SN: 9/29/22). Collectively, the work suggests that the process of becoming a mother, called matrescence, is another stage of development, like the brain overhaul that happens in adolescence (SN: 2/27/23).

Earlier experiments mostly compared brains of women before and after their pregnancies and inferred what happens in between (SN: 12/19/16). “There was a missing piece,” McCormack says. “The nine months of pregnancy was a black box, and we could only guess what that trajectory looks like.” With four MRI scans before pregnancy, 15 scans during pregnancy and seven scans in the two years after the baby was born, the new study follows the entire arc for one mother.

Previous studies have found that the volume of gray matter in the brain, made largely of cell bodies but not predominantly the message-moving tendrils, is smaller after pregnancy than before it. The new study confirms that finding and goes farther, showing the sweeping magnitude of that reduction. Gray matter volume was reduced in about 80 percent of the places in the brain that researchers studied, shrinking on average by about 4 percent of its starting bulk.

A shrinking brain sounds scary, but here, it isn’t, says Emily Jacobs, a cognitive neuroscientist at the University of California, Santa Barbara. In a news briefing September 12, she likened this process to Michelangelo chipping away excess marble to reveal David.

The particular brain under scrutiny belongs to cognitive neuroscientist Liz Chrastil, one of the researchers working on the project. She was planning to undergo in vitro fertilization as she and her colleagues began thinking about studying the brain throughout pregnancy.

Over the course of her pregnancy and afterward, Chrastil says she felt fine as her gray matter was reduced and refined, as the researchers expected. But another change to her brain surprised them all. Some of her brain’s white matter tracts grew stronger, peaking in the second trimester. These tracts are bundles of information-sending fibers that travel around the brain. The stronger they are, the more efficiently they can carry information. By the end of Chrastil’s pregnancy, her white matter tracts had largely returned to their pre-pregnancy strength.

Some of the changes, such as gray matter reductions, seem to be permanent, says Susana Carmona, a neuroscientist at the Instituto de Investigación Sanitaria Gregorio Marañón in Madrid who was not involved in the study. She and others have found evidence of these changes lasting years after pregnancy. “It’s highly probable that these are lifelong,” she says.

For now, the findings lead to more questions than answers, says Chrastil, of the University of California, Irvine. Women’s brains are woefully understudied. “It’s somewhat shocking that we know so little at this point,” Chrastil says.

With her many hours lying in a scanner, Chrastil has done her part to push the science forward. And she’s not ruling out more. “I only have one child,” she says, a four-and-a-half-year-old boy who loves volcanoes and planets. “If I have a second one, I’ll get back in the scanner.”