Pregnancy prepares the brain for parenthood

Abstract

A case study has revealed widespread changes to the maternal brain during pregnancy. This is a milestone in the emerging neuroscience of ‘matrescence’ — the idea that pregnancy is a developmental stage in adulthood.

Graphical Abstract

Brain changes during pregnancy have been mapped in detail for the first time. Writing in Nature Neuroscience, Pritschet et al.¹ report a case study of a single participant who completed magnetic resonance imaging (MRI) scans at 26 timepoints: 4 before pregnancy, 15 during pregnancy and 7 in the first 2 years after childbirth. The researchers detect widespread anatomical changes throughout the brain, which might reflect the refinement of neuronal connections in preparation for birth and caring for a child.

Brain MRI scans can measure changes in the brain’s physical structure, which can often be informative of changes in function. When the authors examined the brain’s cortex, they found that cortical thickness and volume of grey matter (brain tissue that contains neuronal cell bodies and their connections) decreased linearly across pregnancy in almost every region they measured. Decreases were followed by partial gains in the years after childbirth, but not a return to baseline levels.

These findings add to previous evidence from studies comparing brain structure before and after pregnancy, which suggest that there is a pregnancy-related volumetric reduction that persists well beyond delivery². Until now, however, the timing and trajectory of the changes were unknown, and the extent of restructuring, which peaks in the final gestational weeks, had not been seen. This case study also confirms what was previously only hypothesized: that the event of childbirth represents an inflection point (Fig. 1).

Figure 1 |. Brain changes before, during and after pregnancy.

a, Pritschet et al.¹ measured anatomical alterations in the brain using precision magnetic resonance imaging (MRI) at 26 time points over the course of one pregnancy, from pre-conception to two years postpartum. Measurements included thickness of the brain’s cortex; the volume of grey matter (which contains neuronal cell bodies and their connections) in both cortical regions and subcortical regions (such as the hippocampus); and the integrity of white-matter tracts (such as the corpus callosum), which consist of neuronal projections that connect different regions of the brain. b, The authors saw a widespread reduction in grey-matter volume and cortical thickness, and an increase in white-matter tract integrity, until an inflection point at childbirth, after which most changes reversed direction. The changes might reflect cognitive and behavioural adaptations in preparation for childbirth and the demands of caring for a child. (Adapted from Fig. 1 of ref. 1.)

In addition to cortical changes, the authors saw a reduction in grey-matter volume in brain regions beneath the cortex. The subcortical regions showing the most pronounced changes were the same regions that, in mice, are remodelled by exposure to pregnancy hormones and are crucial for inducing maternal caring behaviour³. This supports the interpretation that neural changes during pregnancy occur in service of cognitive and behavioural adaptations to parenting — an interpretation that is bolstered by other evidence that volume reductions relate to positive parenting behaviours, such as mother–infant bonding⁴. Any inclination to interpret gestational reductions in brain volume as a reinforcement of the negative ‘mommy brain’ concept — which describes forgetfulness and brain fog experienced by some individuals before and after giving birth — should therefore be rejected in favour of a narrative about evolutionarily advantageous adaptations that occur at this life transition⁵.

The precision imaging methods used by Pritschet and colleagues enable a nuanced understanding of microstructural changes underlying the anatomical restructuring and rewiring of neuronal connections — known as neural plasticity — that occurs before and after childbirth. Prenatal and postnatal imaging previously found that changes to a part of the brain called the hippocampus can be especially pronounced, and highlighted that the architecture of connections between subregions of the hippocampus should be explored further². In their case study, Pritschet et al. applied specialized microstructural imaging techniques to investigate this connectional architecture in an unprecedented level of detail.

They found that the volumes of hippocampal subregions decreased non-linearly over gestation and did not return to baseline levels in postpartum years. By contrast, the integrity of white-matter tracts (which consist of nerve fibres that allow exchange of information between brain regions) increased throughout pregnancy and returned to baseline. Interestingly, areas that showed substantial white-matter neural plasticity included tracts that facilitate communication between emotional and visual processing hubs. Overall, microstructural evidence from this study provides a detailed picture of how the brain might run through a systematic program of transitional stages leading up to and following delivery.

Perinatal neural plasticity is probably more than just preparation for life after delivery. The clear inflection point in indicators of anatomical change suggests a role for neural plasticity in preparation for the birth itself. Birth involves the orchestration of complex neurobiological processes that allow for successful delivery of the infant. Omitting any consideration of this from interpretations of these brain changes neglects the evolutionary significance of childbirth. Neuroscientific inquiry about the perinatal brain should therefore also consider transient programs of the birthing brain⁶.

Interpretations of the functional significance of neural change have often focused on preparation for caring, in which attention, motivation and sensitivity to infant cues soon after delivery seem to be orchestrated by a multifaceted parental brain network⁷. By depicting reorganization around delivery, the findings from this case study highlight how multiple processes with unique timelines probably contribute to the symphony of change that leads up to and follows childbirth.

This case study is a milestone in the emerging neuroscience of ‘matrescence’, a concept that refers to the transition to motherhood as a developmental stage⁸. Witnessing neural plasticity unfold over the course of one pregnancy will inspire future studies that have more participants and address individual variation in the context of health and disease. Around 17% of people who give birth experience perinatal mood and anxiety disorders, such as postpartum depression⁹. Furthermore, some of the brain networks that show the most pronounced changes with pregnancy, particularly reward circuits and the default mode network (which processes self-referential thought), are also implicated in mood disorders. To understand how perinatal mood disorders arise, it will be crucial to study variation in these brain changes using repeated brain measurements taken over time in a large group of participants.

Future studies should seek to isolate factors that accompany beneficial or detrimental patterns of perinatal neural plasticity, such as hormone functions, inflammatory processes, physiology and environmental, psychological and social factors. These associations will be needed to uncover strategies for optimizing maternal neurological health. Future research will also greatly benefit from including non-birthing parents who are influenced psychologically and socially, but not biologically, by pregnancy.

The fact that scientists are only beginning to attend to the neuroscience of pregnancy reflects an overall dearth of research on women’s health. Emerging brain data finally offer neuroscientific validation of a phenomenon long recognized by birthing parents and echoed by psychoanalysts: that becoming a parent is profoundly transformative.