Pregnancy shrinks parts of the brain, leaving 'permanent etchings' postpartum

Pregnancy may cause more than 80% of the brain's gray matter to shrink, leaving "permanent etchings."

That's what researchers found when a pregnant neuroscientist underwent more than two dozen brain scans throughout her pregnancy and for two years postpartum. After pregnancy, the new mom regained some gray matter, which includes both the cell bodies of neurons and the connections between them. But much seemed to be gone for good.

On average, there was a 4% decrease in gray-matter volume within the affected brain areas, said Emily Jacobs, an associate professor of psychological and brain sciences at the University of California, Santa Barbara (UCSB) and co-senior author of the study.

"That's similar to the amount of reduction in puberty," Jacobs noted at a news conference Thursday (Sept. 12). Hormone surges in puberty come with a dip in gray-matter volume, as the brain prunes excess tissue so it can run more efficiently. Something similar may happen in pregnancy, Jacobs suggested.

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"Sometimes people bristle when they hear that gray-matter volume decreases during pregnancy — like, 'That can't be a good thing,'" she said. However, "this change probably reflects the fine-tuning of neural circuits, not unlike the cortical thinning that happens during puberty."

That fine-tuning may forever change the brain. "Many of these changes seem to be what you might think of as permanent etchings in the brain," Jacobs said.