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Pregnancy causes long-term changes to brain structure, says study

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Decrease in volume of grey matter in certain areas of the brain could help boost a mother’s ability to care for her child, research suggests

Findings suggest there may be an evolutionary purpose to the brain changes, say scientists.
Findings suggest there may be an evolutionary purpose to the brain changes, say scientists. Photograph: Katie Collins/PA

Last modified on Tue 28 Nov 2017 04.07 EST

Pregnancy appears to trigger long-term changes in brain structure, researchers have revealed, suggesting that the transformations could boost a mother’s ability to care for her newborn baby.

The study, based on brains scans, found that the volume of grey matter in certain regions of the brain decreased in women who had been pregnant – a shift that was found to last for at least two years.

“These changes were remarkably consistent,” said Elseline Hoekzema, co-author of the research from Leiden University. “So consistent that a computer algorithm could automatically identify which of the women in our sample had been pregnant between the sessions and which [had] not.”

The research suggests the changes could help mothers understand the needs of their newborn, and influence mother-child attachment. “Brain changes may sound somewhat intimidating, but our findings suggest that there may be an evolutionary purpose to these changes that may serve you in some way when you become a mother,” said Hoekzema.

Writing in the journal Nature Neuroscience, researchers from the Netherlands and Spain describe how they used magnetic resonance imaging (MRI) to compare the brain structure of 25 first-time mothers before and shortly after pregnancy. The scans were also compared with those of 20 women who had not become pregnant, 19 first-time fathers and 17 men without children.

The results reveal that the new mothers experienced a decrease in the volume of grey matter – thought by the authors to imply a fine-tuning of connections – in regions of the brain involved in social processes, with the majority of the changes found to last at least two years after giving birth.

What’s more, the brain regions which showed a drop in grey matter volume were found to overlap with areas linked to the so-called “theory of mind network” –regions of the brain linked to the ability to put oneself in other people’s shoes and imagine how they would think or feel.

“It does make sense that a first time mother is going to have to work really hard to understand their baby’s needs,” said Dr Kirstie Whitaker, an expert in neuroimaging from Cambridge University. “They have theory of mind anyway, they are adult women who are capable of empathising with others, but this is a new stage, this is like another step up in terms of understanding how another being is seeing the world,” said Whitaker, who was not involved in the research.

While there has been much debate over whether pregnancy affects women’s memory, the new study found no differences between the women who became pregnant and the other participants when given a series of verbal and working memory tests. “It is important to stress that our findings do not suggest any link to changes in general cognitive abilities or intelligence,” said Hoekezema.

But the changes in grey matter volume do appear to play a role in levels of attachment between mother and child, the authors note. Furthermore, the areas that showed a drop in grey matter volume partially overlapped with regions of the brain that showed the strongest response when the new mothers were shown images of their new child, compared to other babies.

“These findings provide some [of] the first evidence that these [brain changes] may in some way help a mother to care for her infant,” said Hoekzema.

Despite the study’s small sample size, the research is convincing, says Whitaker. But, she adds, the findings do not necessarily mean that pregnant women are shedding brain cells.

“[It] is not that mothers are losing brain cells, losing grey matter in these regions, it is that they have actually have other cells come in to help reorganize and change up some of those connections to strengthen them, or at least make them more efficient,” she said, pointing to similarities in changes that occur in the teenage brain.

While the researchers say the lack of similar brain changes among new fathers suggests the adjustments are down to biological processes, such as fluctuations in hormones, Whitaker points out that environmental influences could be at play. But she agrees with the authors’ suggestion that decrease in grey matter volume could be linked to evolutionary pressures.
