Brain scans show that some brain regions become smaller and thinner during pregnancy, and that most of these changes reverse after giving birth. This suggests the brain is restructuring itself during and immediately after pregnancy, potentially to prepare for parenthood.
鈥淧regnancy is probably the most intense hormonal event that a human being can go through. So, it was reasonable to think the brain will change during pregnancy,鈥� says at the General University Hospital Gregorio Mara帽贸n in Spain.
Previous studies involving a small number of participants have shown pregnancy alters the structure and organisation of some brain networks. To investigate further, Carmona 聽and her colleagues scanned the brains of 110 first-time mothers during the third trimester of their pregnancy, and again within a month after they gave birth. They also scanned the brains of 34 women who had never had children.
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The researchers found significant changes in the cortex, or the outer region of the brain, during and after pregnancy. On average, the cortex was 2.5 per cent thinner and 4.6 per cent smaller in volume in pregnant women than in those who didn鈥檛 have children. Most of these differences attenuated in the postpartum period, except in two brain networks called the default mode network and frontoparietal network. Regions in these networks were at least 2 per cent thinner and almost 3.6 per cent smaller in volume in new mothers than in women who didn鈥檛 have children.
The default mode network is critical for self-perception and social interaction, and the frontoparietal network is important in executive functions like planning and carrying out tasks. More data is needed to elucidate why pregnancy alters these networks, but one widely accepted hypothesis is these changes help prepare for parenthood, says at Columbia University in New York.
Cortical thinning also occurs during puberty as the brain refines neuronal pathways, a process called synaptic pruning. Think of it like transforming a system of backcountry roads into a network of highways 鈥� some roads are closed off while others are built into efficient speedways. This could be why the cortex thins in pregnancy and postpartum, too, says Monk.
It would make sense for the brain to refine pathways in these regions to facilitate empathising and caring for a child, says Carmona. 鈥淚f you ask any mother, most of them will tell you, 鈥業 feel completely different [after giving birth].鈥� These changes might be behind this feeling, but we still don鈥檛 know,鈥� says Carmona.
Yet, the fact that most cortical changes reverse in postpartum suggests another, more dynamic mechanism is also at play. Carmona believes this might be widespread decreases in microglia, the brain鈥檚 immune cells. 鈥淵our whole immune system has to adapt so you can gestate a person that is genetically different from you, and we know that microglia change shape and number pretty quickly,鈥� she says.
These findings could also help us better understand neurological and mental health conditions associated with pregnancy, like postpartum depression, says Carmona. 鈥淚t鈥檚 important to realise that parenting begins before birth,鈥� says Monk. 鈥淭here鈥檚 so much brain plasticity and change happening that we could get in there, then, to promote optimal wellbeing. And that could help families get off to a better start.鈥�
Nature Neuroscience
