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MRIs taken from before conception until two years after birth show some short-lived changes and some lasting years. 

By Ian Sample, 16 Sep 2024

Profound changes that sweep across the human brain during pregnancy have been captured for the first time, after researchers performed precision scans on a woman carrying her child.

MRI scans taken every few weeks from before conception until two years after childbirth revealed widespread reorganisation in the mother’s brain, with some changes short-lived and others lasting years.

The work, described as “truly heroic” by one independent expert, paves the way for a far deeper understanding of the mother’s brain in pregnancy. Further scans are now being gathered from other pregnant women to learn about the risks of postnatal depression, the link between pre-eclampsia and dementia, and why pregnancy can reduce migraines and symptoms of multiple sclerosis.

Scientists took 26 brain scans of a healthy 38-year-old woman who conceived via IVF, and concurrent blood samples to monitor the dramatic surges in hormones during pregnancy. The data revealed how the brain changed, week by week.

Most apparent was a steady decrease in grey matter, the wrinkly outer surface of the brain, throughout pregnancy and a temporary peak in neural connectivity at the end of the second trimester.

“The maternal brain undergoes this choreographed change across gestation and we’re finally able to observe the process in real time,” said Prof Emily Jacobs, a researcher on the study at the University of California, Santa Barbara.

Scientists have previously taken snapshots of women’s brains at various points in pregnancy, but the latest work shows how these can miss temporary changes that revert to normal by the time the woman gives birth.

Writing in Nature Neuroscience, the lead author, Laura Pritschet, and her colleagues describe how soaring hormones, such as oestrogen and progesterone, drive significant physiological changes in pregnancy, affecting blood plasma, metabolism, oxygen consumption and immunity. The same hormones resculpt the brain.

To understand more, the researchers used precision MRI to scan the brain of Dr Elizabeth Chrastil, a colleague at the University of California, Irvine. She was scanned before conceiving, during pregnancy and for two years after her son was born in May 2020.

“It was quite an intense undertaking,” Chrastil said, but added that she did not feel particularly different in pregnancy. “Some people talk about ‘mummy brain’ and things like that, and I didn’t really experience any of that.”

The scans revealed widespread reductions in grey matter volume and thickness, particularly in regions involved with social cognition. White matter microstructure, a measure of the brain’s wiring, increased to a peak at the end of the second trimester before dropping back down. Cerebrospinal fluid and brain cavities known as ventricles both expanded. The changes were linked to rising hormone levels.

“Sometimes people bristle when they hear that grey matter volume decreases in pregnancy,” Jacobs said. “This change probably reflects the fine tuning of neural circuits, not unlike the cortical thinning that happens during puberty.” The researchers compared the process to the sculpting of Michelangelo’s David from a block of marble.

The study does not explain behaviours or emotions that arise in pregnancy, and many factors beyond hormones, such as stress and sleep loss, are at play. But some brain changes were still present two years after childbirth, hinting at cellular changes in the organ. “This paper really opens up more questions than it answers,” Chrastil said. “We’re really just starting to scratch the surface.”

The work marks the launch of the Maternal Brain Project, an international effort to gather similar scans from more pregnant women. Jacobs said: “There is so much about the neurobiology of pregnancy that we don’t understand yet and it’s not because women are too complicated, it’s not because pregnancy is some Gordian knot, it’s a byproduct of the fact that the biomedical sciences have historically ignored women’s health.”

Gina Rippon, a professor emeritus of cognitive neuro-imaging at Aston University in Birmingham, England, said it was “a truly heroic” project, adding: “The data from this study illustrate just how much we have been missing.”

Dr Ann-Marie de Lange, the leader of the FemiLab group at Lausanne university hospital, called the work “fascinating”. “This approach will not only help us map maternal neuroplasticity, but also identify markers that indicate risk for postpartum depression, a serious condition that often goes untreated,” she said.

(Sources: The Guardian)