Pregnancy changes the brains of expectant mothers

During pregnancy, the structure and function of a woman’s brain changes considerably in certain areas, Dutch research among forty pregnant women shows. These changes may play a role in the nesting urge that many expectant mothers experience at the end of pregnancy, and in the bonding between mother and child after birth. A year after giving birth, many of these changes are back to their pre-pregnancy state. The findings are published Tuesday in the scientific journal Nature Communications.

During pregnancy, unprecedented amounts of hormones bring about major changes in a woman’s body. Some are temporary, others persist for decades after birth.

Changes also occur in the brain, brain researcher Elseline Hoekzema and her colleagues from Amsterdam UMC and Leiden University discovered. They examined forty women before, during and after their first pregnancy, and 28 of them also one year after giving birth. They scanned the women’s brains, made heart films and determined, among other things, the amount of pregnancy hormones in the urine.

Empathy

The researchers discovered that during pregnancy an improved connection occurs in the so-called default mode network, a network of different brain areas that are collectively active in the ‘resting position’, when someone is not doing anything. It is also involved in social interaction and empathy. One area in that network in particular, the cuneus, turned out to be remarkably more functionally connected to the rest of the network among the pregnant women. They also saw that during pregnancy, the gray matter decreases in certain areas of the brain, where the cell bodies of nerve cells are located – an effect that Hoekzema previously found in a study of Spanish women. The researchers found no major changes in the white matter, formed by the long nerve cell extensions.

Hoekzema and her colleagues also administered questionnaires to the participating women. In this they asked, for example, about cleaning behavior and how selective the expectant mother was in her social contacts, in order to determine the degree of nesting urge – ‘nesting’ animals and people prefer to focus on acquaintances. And they used questionnaires to map the mother-child bond.

Gray matter shrinkage in the pregnant women was related to nesting urges in the mothers-to-be, statistical analysis of the data showed. It was also associated with increased levels of the hormone estradiol in the last three months of pregnancy. This study cannot definitively prove a causal relationship, but it suggests that the excessive exposure to estrogen at that stage of pregnancy plays an important role, the authors write. Other things that could possibly affect a pregnant woman’s brain, such as a lot of stress or too little sleep, turned out to be unrelated.

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Binding disorder

The increase in functional compounds in the default mode network was related to another important behavior of the expectant mother: bonding with her child. Mothers with a stronger connection in that network during pregnancy had a better bond with their child a year later. They had more fun interacting with their child, and less rejection, and the risk of a disturbed mother-child bond was lower. Whether a mother breastfed, and the way she had given birth, had no clear effect on this.

“In mother-child bonding disorders, there is a strong hostility towards the child, which manifests itself in complete rejection or aggression. Fortunately, there were no extreme cases in our study, but the extent to which the mothers feel anger or aggression towards their child always varies,” Hoekzema explains by email.

Through this kind of research, Hoekzema hopes to get a better picture of what happens in a pregnant woman’s body, and also what happens if there are problems with the pregnancy or birth. “In the sensitive period around birth, serious mental problems can occur, such as depression, psychosis, or mother-child bonding disorders. It is quite conceivable that these kinds of brain changes contribute to this.”

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