Pregnancy causes profound brain changes, improving maternal instincts and mental health

Scientists are discovering how pregnancy transforms the brain, with changes in gray matter that shape maternal instincts and long-term well-being.

Study: Pregnancy involves a U-shaped trajectory in the human brain structure, linked to hormones and maternal attachment. Image credits: Maridav / Shutterstock

This is evident from a recent study published in the journal Nature communicationresearchers conducted a longitudinal study to investigate the neurological changes associated with human pregnancy, especially in new mothers.

Their research spanned before pregnancy, during pregnancy and postpartum and found that gray matter (GM) volume evolves in a U-shaped pattern: it first decreases in late pregnancy and then recovers over the six months after childbirth. The study found that GM volume decreased by 2.7% during the second trimester and by 4.9% just before delivery, followed by a 3.4% recovery postpartum. Hormonal evaluations suggest that these changes are caused by pregnancy-related estrogen fluctuations, identifying estriol sulfate and estrone sulfate as key factors rather than parenting experience.

Notably, maternal mental health was found to influence the relationship between postpartum GM recovery (volume) and maternal attachment. In particular, maternal well-being mediated more than 50% of the relationship between GM volume recovery and maternal attachment, underscoring its crucial role. These findings provide the first evidence for the previously hypothesized U-shaped GM pattern, fill a significant gap in neuroscience, and lay the foundation for future neuroimaging research to improve maternal mental health and well-being.

Background

Pregnancy is perhaps the most transformative period in a woman’s life, especially in animals that exhibit parental care. More than 140 million women worldwide give birth annually, with previous neuroimaging research showing significant remodeling of brain architecture associated with this. These studies suggest that brain remodeling helps equip pregnant women for motherhood by strengthening their maternal attachment.

Concurrent studies using mouse (rodent) model systems have identified changes in steroid hormones that may facilitate maternal behavior. A recent observation-based hypothesis proposes that human brains may undergo volume evolution of cortical gray matter (GM) during pregnancy and that this volume change may follow a U-shaped pattern of initial loss (during pregnancy) and subsequent gain (postpartum). Unfortunately, this hypothesis and the factors that influence its manifestation (such as hormones, maternal experiences, and mental health) have never been tested.

About the study

The current prospective study aims to address these knowledge gaps using advanced Magnetic Resonance Imaging (MRI), neuropsychological assessments and hormone analyzes across the entire pregnancy spectrum (before, during and after pregnancy and birth). To ensure that the observed patterns were limited to the maternal process, data from expectant mothers (referred to as ‘gestational mothers’; n = 127) were compared with nulliparous women (those who had no pregnancy plans during the study; n = 32) .

In addition, to unravel the role of physiological changes versus the parenting experience, data from gestational mothers were compared with those of “non-pregnant mothers (n=20),” partners of gestational mothers who shared the parenting experience (infant maintenance) without becoming pregnant.

“This groundbreaking design allowed us to uncover the brain pathway that unfolds during the transition to motherhood, as well as its link to steroid hormones and maternal attachment, filling a critical gap in the literature on the human maternal brain.”

The study was conducted over five sessions – before conception, the second trimester, the third trimester, one month postpartum and six months postpartum. Each session consisted of a comprehensive MRI evaluation, urine sample collection (for hormone/endocrine assessments), and mental health questionnaires. The MRIs are optimized to scan and image global cortical GM volume, surface area, and thickness, providing a comprehensive assessment of brain changes.

MRI data combined with quantification of urine-derived steroid metabolites were used to unravel the associations between brain structural evolution and pregnancy hormones. Of the 49 hormones analyzed, only estriol sulfate and estrone sulfate showed significant negative correlations with volume changes of GM, suggesting their role in inducing or modulating outcomes of interest. Finally, questionnaire and mental health data were used to assess parental experiences and the contribution of psychological well-being to observed neurological evolution.

Findings of the study

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

GM volume recovered by 3.4% at 6 months postpartum but did not fully return to pre-pregnancy levels, indicating possible long-term adjustments. Although longer follow-up periods are needed to confirm this hypothesis, current study data suggest that changes in GM volume during a woman’s first pregnancy may have lifelong consequences, permanently equipping her for motherhood via improved maternal attachment. GM volumes remained unchanged in nulliparous and non-pregnancy cohorts.

Coupled evolution analyzes 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 mirrored manner, which underlines the role of sulfated estrogens in the suggests illness. producing or modulating interesting outcomes.

Finally, evaluations of the interplay between structural changes in the brain, maternal mental health (maternal well-being, postnatal depression and perceived stress) and infant attachment revealed interesting results:

1. Greater recovery of GM after delivery was positively associated with reduced hostility toward the baby,
2. Maternal well-being directly increased the magnitude of postpartum GM recovery (and in turn influenced the initial outcome), and
3. Postnatal depression and perceived stress were not significantly associated with changes in maternal affection or GM volume.

Conclusion

The current study is the first to confirm that women undergo substantial GM volume changes during pregnancy, observed as a U-shaped pattern of initial prepartum loss and subsequent postpartum gain. Estrogens, particularly estriol sulfate and estrone sulfate, are likely the driving force behind these changes, with rearing experience playing little to no role in structural changes in the brain. Furthermore, functional connectivity analyzes revealed no significant changes in network modularity, segregation, or participation coefficient across the gestational period.

Maternal well-being emerged as the strongest determinant of postpartum GM recovery and, in turn, maternal attachment, mediating more than half of the observed effect.

“By revealing the dynamic brain changes during pregnancy, the possible hormonal factors behind these changes, and how their interplay impacts maternal psychological well-being, this study marks a crucial advance in maternal brain research.”