The brains of first-time mothers undergo significant changes in volume and thickness during late pregnancy and the early postpartum period, according to new research published in Nature Neuroscience. These findings, based on the largest longitudinal neuroimaging study of mothers to date, provide unprecedented insight into the dynamic nature of the maternal brain, shedding light on how pregnancy and childbirth impact brain structure.
Earlier studies hinted that pregnancy and the postpartum period are times of significant brain changes. These studies, however, presented mixed results: some suggested brain volume decreased during pregnancy, while others found increases postpartum. This lack of clarity spurred the recent investigation, aiming to chart a more detailed map of how motherhood affects the brain.
“The transition to motherhood is a transformative event that affects almost half of the world’s population, yet it has been largely unexplored from a neuroscientific perspective. It is urgent to approach the topic. Indeed, current evidence positions pregnancy as a period of enhanced neuroplasticity in adult life with important implications for women’s brain health and brain aging trajectories,” said study author Susana Carmona, the head of the NeuroMaternal Lab at the Instituto de investigación Sanitaria Gregorio Marañón and author of the book “NeuroMaternal.”
The researchers employed a case-control longitudinal design, allowing them to track and compare changes in brain structure over time between two distinct groups: first-time mothers and nulliparous women (women who have never given birth). The main dataset included 110 first-time mothers, alongside 34 nulliparous women serving as the control group. To validate and bolster their findings, the researchers conducted a replication study with an independent group comprising 29 first-time mothers and 24 control participants.
The primary tool for data acquisition was magnetic resonance imaging (MRI), a non-invasive imaging technique that provides detailed images of the brain. The MRI sessions were scheduled at two critical points: late pregnancy (during the third trimester) and early postpartum (within the first month after birth).
One of the most striking results was the observation of decreased global cortical volume and thickness in first-time mothers during late pregnancy, compared to nulliparous women. This reduction was not confined to a specific area but was widespread, affecting midline regions such as the medial prefrontal gyrus, anterior and posterior cingulate, and lateral areas including the precentral and postcentral sulci, dorsolateral prefrontal cortex, and the temporoparietal junction.
In the early postpartum period, these differences in cortical volume and thickness persisted, though the extent of the affected areas was reduced. The findings suggest that the brain’s cortical structure undergoes significant adaptation during the transition to motherhood.
Carmona and her colleagues also observed a significant increase in global cortical volume, thickness, and surface area from late pregnancy to early postpartum among the mothers. This increase was particularly notable in areas such as the posterior cingulate, paracentral gyrus, precuneus, and lateral regions like the precentral and supramarginal gyri, and the superior temporal gyrus. The extent of these increases correlated with the percentage of postpartum time, indicating a recovery or compensatory phase in the early postpartum period.
The type of childbirth also impacted these changes: mothers who had a scheduled cesarean section without experiencing labor showed larger increases in cortical volume, thickness, and surface area postpartum than those who went through labor. The results indicate that the series of changes in the immune and hormonal systems during labor might also trigger changes in the brain’s ability to adapt and reorganize itself.
“Pregnancy, childbirth, and postpartum are characterized by very different hormonal, immunological, and environmental processes,” Carmona told PsyPost. “This study has enabled us to identify that these three stages also involve distinct neuroplasticity mechanisms, thus highlighting the necessity to evaluate how each of them uniquely shapes the maternal brain.”
The new findings are in line with a previous study, which found evidence that pregnancy leads to specific structural and functional brain adaptations, potentially facilitating the mother-infant bond and preparing the mother for new maternal roles. That study found significant reductions in grey matter volume in pregnant women, affecting areas like the prefrontal and temporal cortex, without significant changes in white matter. Additionally, pregnancy induced selective functional changes, notably an increase in coherence within the Default Mode Network (DMN), particularly in the cuneus, which is linked to visual processing and self-referential tasks.
In addition to MRI, Carmona and her colleagues incorporated a range of neuropsychological evaluations. Participants completed questionnaires before each MRI session, providing data on various factors such as sleep quality, perceived stress, depression symptoms, and maternal attachment.
During the postpartum period, first-time mothers experienced increased levels of perceived stress, sleep problems, and symptoms of depression compared to their levels during pregnancy. Higher levels of anxiety during pregnancy were associated with a more challenging childbirth experience and increased maternal stress about parenting during the postpartum period. A more difficult childbirth experience also correlated with higher perceived stress levels and postpartum maternal stress.
In addition, the researchers found that increased stress and maternal stress from pregnancy to postpartum were linked to higher scores of postpartum depression and lower levels of maternal attachment. Worsening depression scores from pregnancy to postpartum were associated with increased sleep problems and reduced maternal attachment.
But the study, like all research, includes some limitations. One of the primary limitations was the absence of pre-pregnancy brain data, which would have provided a baseline for comparison. Additionally, the study did not include biomarkers of the endocrine and immune systems, which are believed to play a significant role in regulating brain changes during pregnancy.
“As a relatively new topic, there are still many questions to be answered,” Carmona said. “One of our future objectives is to track the complete trajectory of brain changes from preconception to several years postpartum. From a clinical perspective, establishing the foundations of the human maternal brain is essential to advance in predicting and treating perinatal mental health disorders.”
“This study would not have been possible without the work of María Paternina-Die and Magdalena Martínez-García, the first two authors of the publications, as well as the rest of the coauthors.”
The study, “Women’s neuroplasticity during gestation, childbirth and postpartum“, was authored by María Paternina-Die, Magdalena Martínez-García, Daniel Martín de Blas, Inés Noguero, Camila Servin-Barthet, Clara Pretus, Anna Soler, Gonzalo López-Montoya, Manuel Desco, and Susana Carmona.