Profound changes that sweep through the human brain during pregnancy have been captured for the first time after researchers carried out precision scans on a woman carrying her child.
MRI scans taken every few weeks from before conception to two years after delivery revealed widespread reorganization in the mother’s brain, with some changes short-lived and others lasting years.
The work, described by one independent expert as “truly heroic”, paves the way for a much deeper understanding of the mother’s brain during pregnancy. Further scans are now being collected from other pregnant women to learn about the risks of postnatal depressionthe link between pre-eclampsia and dementiaand why pregnancy can reduce migraines and symptoms of multiple sclerosis.
Scientists took 26 brain scans of a healthy 38-year-old woman who became pregnant through IVF, and simultaneous blood samples to monitor the dramatic increases in hormones during pregnancy. The data revealed how the brain changed week by week.
Most evident was a steady decline in gray matter, the wrinkled outer surface of the brain, during pregnancy and a temporary peak in neural connectivity at the end of the second trimester.
“The maternal brain undergoes this choreographed change over pregnancy and we are 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 pictures of women’s brains at various points in pregnancy, but the latest work shows how they can miss temporary changes that return to normal by the time the woman gives birth.
Write in Nature Neurosciencelead author Laura Pritschet and her colleagues describe how rising hormones, such as estrogen and progesterone, drive significant physiological changes in pregnancy, affecting blood plasma, metabolism, oxygen consumption, and immunity. The same hormones regenerate 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 pregnancy, 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 didn’t feel particularly different during pregnancy. “Some people talk about ‘mummy brain’ and things like that, and I haven’t experienced any of that.”
The scans revealed widespread decreases in gray matter volume and thickness, particularly in regions involved in social cognition. White matter microstructure, a measure of the brain’s wiring, increased to a peak at the end of the second trimester before declining. 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 gray matter volume decreases during pregnancy,” Jacobs said. “This change likely reflects the fine-tuning of neural circuits, not unlike the cortical thinning that occurs during puberty.” The researchers compared the process to sculpting Michelangelo’s David from a block of marble.
The study does not explain behavior or emotions that arise during pregnancy, and many factors outside of hormones, such as stress and sleep loss, are at play. But some brain changes were still present two years after delivery, indicating cellular changes in the organ. “This paper really opens up more questions than it answers,” Chrastil said. “We’re really just beginning to scratch the surface.”
The work is the introduction of the Mother Brain Projectan international effort to collect similar scans from more pregnant women. Jacobs said: “There is so much about the neurobiology of pregnancy that we still don’t understand and it’s not because women are too complicated, it’s not because pregnancy is some kind of Gordian knot, it’s a byproduct of the fact that the biomedical sciences have historically ignored women’s health.”
Gina Rippon, an emeritus professor of cognitive neuroimaging at Aston University in Birmingham, England, said it was a “truly heroic” project, adding: “The data from this study just illustrates how much we’ve been missing.”
Dr Ann-Marie de Lange, the leader of the FemiLab Group at Lausanne University Hospitalcalled 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.
