How does pregnancy affect a woman's brain?

A recent study indicates that changes can occur in the structure and function of a woman’s brain when she is pregnant. These changes may prepare the woman for the arrival of her baby.

Pregnancy is an extreme biological process that causes unprecedented endocrine changes in a woman's body. However, the impact of pregnancy on the human brain has long been an under-explored field.

A study published in the journal Nature communicationsreveals that the brain structure of a woman is modified by the release of hormones during pregnancy. Specifically, the release of oestradiol (a female sex hormone) reaches a peak in the third trimester of pregnancy. These changes predispose women to certain maternal behaviours, such as bonding with the baby or preparing the home for the arrival of the newborn.

The study followed 40 women before, during and after childbirth to observe changes in their brains using imaging tests, such as magnetic resonance and scans. Changes in the structure and components of the brain, as well as in the organisation of neurons, were investigated in pregnant women. The results found were an increase in activity of the default mode network and a decrease in grey matter, with no significant changes in white matter. This all occurred as a consequence of hormonal changes.

Grey matter plays an important role in muscle control and the execution of tasks such as seeing, listening, processing memories and emotions and making decisions. The brain also contains white matter, which is involved in motor and sensory function. The grey matter is the nucleus of the neuron, while the white matter consists of the highways that carry the information. The default mode network (DMN) is a set of interconnected regions responsible for much of the brain activity while the mind is at rest.

In 2016, the same author, Dr Elseline Hoekzema, a neuroscientist at Leiden University in Holland, published a study in Nature Neuroscience that showed some changes in the brain structure of pregnant women. The study found that grey matter in the brains of women who had recently given birth seemed to shrink in certain areas, with those changes persisting for up to 2 years after birth.

In this study, it was seen that white matter did not change at all during the pregnancy or subsequent motherhood; however, the volume of grey matter was reduced. This does not mean a loss of functions or memory, but rather a selection of the best neural connections, as also happens in adolescence. Dr Hoekzema says, "It is a process that removes certain connections between brain cells to encourage new connections, and this could help people focus on specific behaviours or activities, such as caring for a baby."

Another study published in 2021 in the journal Brain Sciences concluded that the reduction in volume of the brain's grey matter occurring in pregnancy persists for up to 6 years after childbirth. It was also seen that brain changes were associated with the mother-child relationship, following contact with the baby after delivery. These findings open up the possibility that brain changes in women are permanent; thus, the intention is to encourage neuroimaging studies to include information related to pregnancy, to be taken into account as another variable of interest.

The brain is the most complex organ in the human body; so much so that researchers are still studying how to treat many diseases that affect it. In addition, the brain during pregnancy is in one of its most “plastic” phases, with more neuronal growth and greater connections between neurons; so studies such as these represent an attempt to understand the changes that occur in women’s brains and perhaps, in the long-term, find solutions to problems like postnatal depression.