Pregnant women’s brains shed grey matter to prepare for motherhood, study suggests

Expectant mothers often complain about experiencing “baby brain” – a frustrating forgetfulness and mental fog that can settle in during pregnancy. Misplaced keys, forgotten appointments and lapses in concentration are so common that the term has become part of everyday conversation.

But new research suggests there may be a biological basis behind the phenomenon. A recent study found that grey matter volume in the brain – the part of the brain involved in processing information, emotions and empathy – actually decreases by an average of nearly five per cent during pregnancy.

While shedding brain matter may seem like a cause for concern, scientists in Spain from the Bemother project found that the reduction in grey matter is conducive in helping mothers care for their newborns better.

Prof Susana Carmona, from the Gregorio Marañón Health Research Institute in Madrid, who co-led the study, said: “I like to use the metaphor of pruning a tree. Some of the branches are cut to make it grow more efficiently.”

The brains of 127 pregnant women from Madrid and Barcelona were scanned before, during and after pregnancy – specifically, before conception, at the second and third trimesters of pregnancy, one month after birth and six months after birth.

The scans were then compared to 32 women who were not expecting.

The pregnant women lost an average of nearly five per cent of grey matter – changes which affect 94 per cent of the brain, especially regions linked to social cognition.

The bigger the changes in the brain, the more likely the women were to say they were bonding well with their babies.

Urine and saliva samples were also collected from the women on five occasions, and the scientists found that rising oestrogen levels tracked closely with the reduction in grey matter.

The researchers found that the grey matter partially returned six months after giving birth, but not fully.

The study found that the percentage of grey matter volume recovery during postpartum was associated with a “higher absence of hostility” towards the baby at six months postpartum.

The authors wrote: “This positive association suggests that the brain remodeling experienced by gestational mothers might be adaptive, facilitating facets of maternal behaviour.”

The researchers also found that the neuroanatomical changes occurring after pregnancy affect the mental well-being in mothers, which in turn facilitates adaptive maternal attachment.

The research showed that the mother’s general well-being mediates more than 50 per cent of the relationship between grey matter volume recovery and attachment at six months postpartum.

Building a roadmap to the brain neurological changes during pregnancy and postpartum could help women’s maternal mental health and identify specific periods where interventions could have the greatest impact on psychological well-being.

The study was published in the journal Nature Communications.