Pregnancy causes profound changes in the brain, strengthening maternal instincts and mental health

In a recent study published in the journal researchers conducted a longitudinal study to examine the neurological changes that accompany pregnancy in humans, particularly for first-time mothers.

Their study looked at the period before, during and after pregnancy and found that gray matter (GM) volume evolves in a U-shaped pattern, first decreasing in late pregnancy and then returning to normal within six months after delivery. The study found that the amount of GMOs decreased by 2.7% in the second trimester and by 4.9% immediately before delivery, followed by an improvement of 3.4% after delivery. Hormonal studies suggest that these changes are due to pregnancy-related estrogen fluctuations, with estriol sulfate and estrone sulfate being identified as the key factors, rather than parenting experience.

Of note, maternal mental health has been found to influence the relationship between postpartum recovery (volume) and attachment to the mother. Specifically, maternal well-being mediates over 50% of the association between GMO volume recovery and maternal attachment, highlighting its key role. These findings provide the first evidence for the previously hypothesized U-shaped GM pattern, filling a significant gap in neuroscience knowledge and laying the foundation for future neuroimaging research to improve maternal mental health and well-being.

Background

Pregnancy is perhaps the most transformative time in a woman’s life, especially for parenting animals. Every year, more than 140 million women give birth to babies around the world, and previous neuroimaging studies have shown that this process is accompanied by significant remodeling of brain architecture. These studies suggest that brain remodeling helps pregnant women prepare for motherhood by strengthening their attachment to their mothers.

Concurrent studies in mouse models (rodents) have demonstrated changes in steroid hormones that may facilitate maternal behavior. A recent hypothesis based on observations posits that the human brain may undergo evolution in cortical gray matter (GM) volume during pregnancy and that this volume change may follow a U-shaped pattern of initial loss (during pregnancy) and subsequent gain. (after giving birth). Unfortunately, neither this hypothesis nor the factors that influence its manifestation (such as hormones, maternal experiences, and mental health) have ever been tested.

About the study

This prospective study aims to address these knowledge gaps using state-of-the-art magnetic resonance imaging (MRI), neuropsychological assessments, and hormonal analyzes across the full spectrum of term pregnancy (before, during, and after pregnancy and delivery). To ensure that the observed patterns were limited to the maternal process, data from expectant mothers (called “pregnant mothers”; n = 127) were compared to nulliparous women (those who did not plan to become pregnant throughout the study period; n = 32) .

Furthermore, to uncover the role of physiological changes versus parenting experience, data from pregnant mothers were compared with data from “non-pregnant mothers (n = 20),” partners of pregnant mothers who shared parenting (infant maintenance) experiences. , without being pregnant.

“This groundbreaking project allowed us to uncover the brain trajectory that develops during the transition to motherhood, as well as its relationship to steroid hormones and maternal attachment, filling a critical void in the human maternal brain literature.”

The study was conducted during five sessions – before conception, in the second trimester, in the third trimester, one month after delivery and six months after delivery. Each session included a comprehensive MRI assessment, urine sample collection (for hormone/endocrinology assessment), and mental health questionnaires. MRI images were optimized to scan and image the global volume, surface area, and thickness of the GM cerebral cortex, providing a comprehensive assessment of brain changes.

MRI data combined with quantification of urinary steroid metabolites were used to unravel links between the evolution of brain structure and pregnancy hormones. Of the 49 hormones analyzed, only estriol sulfate and estrone sulfate showed significant negative correlations with changes in GMO volume, suggesting their role in inducing or modulating the outcomes of interest. Finally, questionnaire data and mental health records were used to assess parental experiences and the impact of mental well-being on observed neurological evolution.

Research results

This study is the first to confirm the increasingly popular hypothesis that the amount of GMOs evolves in a U-shape during pregnancy. The volume of GMOs decreases in the second trimester of pregnancy (by 2.7%) and immediately before pregnancy (by 4.9%). These changes were symmetrical in both hemispheres of the brain, with the most significant decreases in the default mode and frontoparietal brain regions.

The amount of GMOs increased by 3.4% six months after giving birth, but did not fully return to pre-pregnancy levels, suggesting possible long-term adaptations. Although longer periods of follow-up are needed to confirm this hypothesis, current research data suggest that changes in the amount of GMOs during a first pregnancy may have lifelong effects, permanently preparing her for motherhood through a strengthened attachment to her mother. GMO volume remained unchanged in the nulliparous and nonpregnant cohorts.

Related analyzes of evolution between neuroanatomical observations (MRI scans) and hormone quantification (analysis of 49 hormones) revealed that only two hormones, estriol sulfate and estrone sulfate, were negatively correlated with GM volume in a temporally reflected manner, suggesting a role for sulfated estrogens in triggering or modulating outcomes of interest.

Finally, the assessment of the interrelationships between structural changes in the brain, maternal mental health (maternal well-being, postpartum depression and perceived stress) and attachment to the child revealed interesting results –

1. Greater GMO recovery after delivery was positively associated with reduced hostility towards the child,
2. Maternal well-being directly increased the extent of recovery from GMO delivery (and in turn influenced the first result) and
3. Postpartum depression and perceived stress were not significantly associated with changes in maternal affection or GMO volume.

Application

This study is the first to confirm that women undergo significant changes in GMO volume during pregnancy, which is observed as a U-shaped pattern involving an initial loss before delivery and a subsequent gain postpartum. Estrogens, particularly estriol sulfate and estrone sulfate, are likely the cause of these changes, and parenting experience plays little or no role in brain structural modifications. Furthermore, functional connectivity analyzes did not reveal any significant changes in network modularity, segregation, or participation rates during pregnancy.

Maternal well-being was found to be the strongest determinant of gene-related postpartum recovery and, consequently, attachment to the mother, mediating over half of the observed effect.

“By revealing the dynamic changes in the brain during pregnancy, the possible hormonal factors behind these changes, and how they interact with each other on maternal psychological well-being, this study represents a key advance in maternal brain research.”