Pregnant woman's grey matter shrinks by 5%, partly recovers postpartum, study finds

New Delhi: Grey matter volume shrinks by about five per cent during pregnancy, followed by a partial recovery in the postpartum period, a study has found.

The changes in grey matter were observed in 94 per cent of the brain, particularly prominent in the default mode network, which is known to help with social cognition. The findings are published in the journal Nature Communications.

Grey matter, which makes up the outermost layer and interior parts of the brain, helps with processing and interpreting information, thereby allowing one to think, learn and remember.

Researchers, led by those from the Universitat Autònoma de Barcelona, Spain, also found that a greater recovery of grey matter was related to a better mother-infant bond.

The team analysed MRI brain scans of nearly 180 first-time pregnant women to study the structural changes occurring during the second and third trimester and the first six months postpartum. Scans taken prior to conceiving served as 'baseline'.

"We unveil a U-shaped trajectory in grey matter volume, which dips in late pregnancy and partially recovers during postpartum," the authors wrote.

"The U-shaped trajectory of GM volume affected numerous regions across the brain's cortex, encompassing 94 per cent of its surface. Particularly striking changes were observed in higher-order cognitive networks such as the default mode and frontoparietal networks," they wrote.

The study also showed that the pregnancy-linked brain changes were related with fluctuating levels of two estrogens -- 'estriol-3-sulfate' and 'estrone-sulfate'. Estrogens are hormones important for sexual development and reproduction in women, and known to rise markedly during pregnancy before returning to basic levels after delivery.

Further, the researchers observed that a higher increase and subsequent decrease in estrogen levels is associated with a greater decrease and subsequent recovery of brain gray matter volume.

The study group also included 'non-gestational mothers' -- women whose partners underwent pregnancy -- and thus, helped determine that the brain changes are largely linked to the biological process of pregnancy, rather than to the experience of becoming a mother, the researchers said.

A study, published in September 2024 in the journal Nature Neuroscience, that tracked neuroanatomical changes before, during and after pregnancy in a 38-year old healthy woman, had found widespread decreases in grey matter which were significantly correlated with rising levels of estradiol (an estrogen).

While some of the brain changes were found to persist up to two years post-pregnancy, others returned to levels similar to those when the woman was two months pregnant.