By Kerstin Dörflinger

Vilarroya and his team study how pregnancy reshapes the maternal brain, following first-time pregnant women and a group of same-sex partners through pregnancy and early motherhood. Their project BeMother sheds light on the mechanisms that enable mothers to meet the demands of caring for their newborns. Each year, nearly 140 million women worldwide experience these remarkable changes, embarking on a life-altering journey that science is only beginning to comprehend fully.

When Vilarroya applied for an ERC grant, the effects of pregnancy on the brain were largely understudied. He attributes this to two main factors: first, a gender bias in science, where research on pregnancy and motherhood received little attention. Second, studies involving pregnant women were often seen as taboo—considered too delicate or even risky to investigate.

In the past, Vilarroya mainly studied children with ADHD, but in 2008, the idea of researching the brains of pregnant women came up. Together with his three female PhD students, he explored how much the topic had been studied. ‘It was crazy because we were convinced that there must be studies on the topic, but there were hardly any,’ he recalls. This gap in research led him to apply for an ERC grant, and in 2019, he was awarded an ERC Advanced Grant for his research idea.

Originally, Vilarroya had planned to recruit women for the project through hospitals and fertility clinics. But then the COVID-19 pandemic hit in 2020, and this plan no longer worked out. ‘It was really hard because everything was closed all of a sudden, and we could no longer recruit women as planned. Instead, they decided to use Instagram to find women willing to participate, which worked very well. They also approached fertility clinics to help find women who had started testing before becoming pregnant with their first child.

Changes in brain structure 

Vilarroya and his team examined women before, during, and after pregnancy using brain imaging, hormonal analyses, and psychological evaluations.

They discovered significant changes in brain structure and function during pregnancy. -One key finding was a U-shaped pattern in the brain’s grey matter volume: it decreased by about 5% during pregnancy, particularly in the second trimester, and partially recovered - by around 3.4% - within six months after childbirth. However, grey matter volume did not fully return to pre-pregnancy levels. These changes were observed in 94% of the brain’s total grey matter volume, especially in regions involved in thinking and social behaviour.

The changes weren’t just structural - pregnancy also influenced the functioning of the brain. Networks such as the default mode and the frontoparietal networks – important for higher-level thinking and social interactions - showed stronger connections after childbirth. These functional changes likely help mothers bond with and care for their babies by making brain communication more efficient.

‘There is clearly a reorganisation of the brain,’ Vilarroya explains, stressing that they found no evidence of cognitive declines, such as a loss of working memory in mothers. The idea that women become more forgetful after childbirth is anecdotal rather than scientifically proven. ‘When you have a baby, things that once seemed important become less so because you now have much more information to process. Your focus changes because you need to pay more attention to your baby,’ he says.

‘All of this probably means that the brain is simply reorganising for different tasks, which a woman faces as she becomes a mother’, he concludes, adding that the brain probably changes forever. 

Hormonal shifts

What drives these changes? Vilarroya's study points to hormonal shifts, especially changes in two types of oestrogens - estriol and estrone sulfate. The study shows, for the first time, that changes in those hormones mirror the pattern of grey matter changes. This aligns with findings from animal studies suggesting that pregnancy hormones play a key role in reshaping the brain for motherhood.

Furthermore, there are indications that the amount of sulfate hormones might influence a mother’s mental health after birth. ‘It might be that oestrogens are protective against postpartum depression, but more studies need to test this hypothesis further’, Vilarroya says.

The researchers also observed a connection between grey matter recovery and both a lack of hostility toward the child and a stronger attachment to the baby. Vilarroya: ‘You could say that the mother’s brain recovery during postpartum period is related to better mental health, which in results in a stronger attachment to the baby.’

The study also examined same-sex partners to see whether there were any differences compared to non-pregnant women. The researchers compared the brains of non-gestational mothers (partners of the pregnant women) and women who hadn’t experienced pregnancy with those of biological mothers. The results confirmed that the brain transformations were unique to pregnancy, as non-gestational mothers and women who hadn’t been pregnant showed no similar changes.

They also found no differences in the results based on the sex of the baby or whether the birth was natural or by Caesarean section.
 

Like a family

‘Those are just the first results of our ERC-funded project’, Vilarroya continues. ‘We will soon publish more results, analysing, for example, the interaction between mother and baby six months after birth. Working with nearly 500 women who participated in the project has been a great experience. ‘We are like a big family now because we have seen each other regularly. We also meet up again with their kids to share the study's results with them.’ Having the collaboration of all these mothers throughout the project was simply ‘fantastic’, the researcher concludes.

Biography

Oscar Vilarroya, MD, PhD, is a Research Director in the Department of Psychiatry at the Autonomous University of Barcelona, Spain. He leads a Cognitive Neuroscience and Neuroimaging lab at the university and the Hospital de Mar Research Institute in Barcelona. His lab has made pioneering contributions to neuroscience, including the first description of neural changes induced by pregnancy, published in Nature Neuroscience. He has been awarded an ERC Advanced Grant for research on this topic. Additionally, Vilarroya has developed research projects in social neuroscience, securing funding from the FP7 and H2020 programs.