There is strong evidence that a mother’s depression during pregnancy tends to be associated with later psychological difficulties for her child, including the child’s own depression. Are these later difficulties linked to infant development in utero and so directly related to the prenatal depression? Or are the child’s difficulties more associated with its experiences after birth, perhaps to a continuation of the mother’s depression, postpartum? Recent research suggests some answers to these questions.
Researchers from the National University of Singapore looked for clues in the brain structure of forty-two infants at the age of 6 months, comparing those whose mothers experienced prenatal depression with those whose mothers did not. They were particularly interested in the amygdala, a brain region that plays a central role in the processing of emotions and memory. Both the size and the functioning of the amygdala are found to be altered in children and adults who experience major depression and other mood disorders. The researchers looked for alterations in the amygdala of infants in this study and for any correlation with prenatal depression in their mother. In order to rule out the effect of the mother’s depression after birth, they also checked for the presence of postnatal depression.
Analysis of the infants’ fMRI scans did show a correlation between having a mother who had experienced prenatal depression and increased connectivity of the left amygdala with brain regions concerned with activating and regulating emotional states.
Infants born to mothers with higher levels of depressive symptoms during pregnancy showed greater functional connectivity of the left amygdala with (i) the bilateral medial prefrontal cortex (mPFC), including ACC, medial orbitofrontal cortex and ventromedial prefrontal cortex, and left insula in the emotional regulation network; (ii) the left superior, middle and temporal cortex in the sensory and perceptual systems; (iii) the left entorhinal cortex in the emotional memory network.
These increased levels of connectivity are similar to those found in adults and adolescents who experience major depression. The association between this changed connectivity and prenatal depression remained significant even after allowing for the presence of postnatal depression and for other factors, such as household income, birth weight and sex.
Infants born to mothers who experienced prenatal depression are themselves more likely to experience depression later in life. While it might be that these mothers were also depressed post partum and that this affected their child, this study suggests that the infant’s susceptibility to depression was related to their mother’s depression before birth.
While showing an association does not prove a causal connection, it is known that the intrauterine experience of the fetus does impact upon its brain development. For example, animal studies show that the raised cortisol levels of stressed mothers during pregnancy leads to changes in their offspring’s amygdala. These changes may prepare the offspring to be more alert to the environmental threats that are stressing the mothers. Depressed human mothers also show raised levels of cortisol during pregnancy and this could provide one possible explanation for the association found in this study. While the changes within brain structure seen in these infants may prepare them to be alert to threats, they may also increase their vulnerability to depression.
This study provides yet more evidence for the importance of perinatal mental health services. The Royal College of Midwives has welcomed the additional funding for such services announced in the recent budget, but has called for this investment to be increased and sustained.
A report on the study can be found in Translational Psychiatry.