Research reveals only a few brain regions remain untouched by transition to motherhood

By Pooja Toshniwal PahariaReviewed by Danielle Ellis, B.Sc.Sep 17 2024

A pioneering study shows pregnancy causes significant brain changes, shrinking regions like the cortex while enhancing connectivity. 

In a recent study in Nature Neuroscience, researchers explored neuroanatomic changes in the human brain during pregnancy.

Background

Pregnancy is a time of extraordinary neuroplasticity, demonstrating the brain's potential to undergo adaptive, hormonally-driven neuroanatomical changes after puberty. During gestation, the mother's body makes physiological changes to assist fetal growth, such as increases in metabolic rate, serum volume, oxygen needs, and immunological control. Considerable elevations in hormone synthesis, particularly progesterone and estrogen, rapidly alter and rearrange central nervous system (CNS) tissues. However, the alterations in the mother's brain during gestation are unclear.

About the study

The present precision imaging study mapped neural changes in the maternal brain during pregnancy.

A primiparous lady aged 38 had 26 magnetic resonance imaging (MRI) scans and blood samples between three weeks preconception and two years postpartum. She had no pregnancy difficulties, had vaginal full-term delivery, and breastfed for 16 months post-delivery. She did not smoke and had no prior head trauma, endocrine abnormalities, or neuropsychiatric diseases.

Researchers performed high-resolution diffusion imaging and segmented the medial temporal lobe (MTL). They analyzed T1-weighted and diffusion MRI scans to study the whole brain and T2-weighted scans to assess MTL changes. Correlational tractography analyzed the association between white matter structure and gestational week. Quantitative anisotropy (QA) assessed white matter changes and tract integrity in the maternal brain. Scanning took place from 9:00 am to 2:00 pm.

MRI quality control assessments included the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and coefficient of joint variation (CJV). Ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) determined serum estradiol and progesterone concentrations before, during, and after pregnancy. The Perceived Stress Scale (PSS), Profile of Mood States (POMS), Pittsburgh Sleep Quality Index (PSQI), and State-Trait Anxiety Inventory (STAI) monitored lifestyle measures and mood.

Researchers compared the neural changes in the maternal brain to those among eight densely sampled controls. General additive models determined associations between summary brain metrics and the gestational week. Linear regressions determined the relationship between endogenous sex hormones and brain subregion volumes.

Results and discussion

The team noticed significant declines in cortical gray matter volume (GMV) and cortical thickness (CT) in the maternal brain as the gestational week progressed and sex hormone production increased dramatically. However, their levels have partially recovered postpartum. Eighty percent of the regions of interest (ROI) (n=400) had a negative correlation between GMV and gestation week. The sensory, attention, and default mode networks showed significant GMV alterations during pregnancy.

In contrast, as the gestational week progressed, the white matter global microstructural integrity, lateral ventricle volume, and cerebrospinal fluid (CSF) increased but dropped postpartum. White matter tracts with robust associations with the week of gestation included the arcuate fasciculus, corpus callosum, inferior longitudinal fasciculus, inferior frontal-occipital fasciculus, superior and middle longitudinal fasciculus, cingulum bundle, corticospinal, corticopontine, and corticostriatal. These tracts provide communication between the emotional and visual processing centers.

Subcortical structures, including the bilateral caudate, ventral diencephalon, thalamus, hippocampus, left putamen, and brain stem, significantly reduced in volume across gestation. MTL segmentation revealed decreased parahippocampal cortex (PHC) and hippocampal CA1, CA2, and CA3 volumes. However, the hippocampal body and parahippocampal gyrus remained largely unaltered.

Neuroanatomical brain alterations significantly correlated with serum sex hormone levels. Serum estradiol and progesterone levels rose considerably throughout pregnancy and decreased abruptly after birth. Estradiol levels were 3.4 pg/mL before conception, increased to 12,400 pg/mL three weeks before birth, and decreased to 11.5 pg/mL three months later. The corresponding progesterone levels were 0.8 ng/mL, 103 ng/mL, and 0.04 ng/mL, respectively.

Pregnancy-related neuroanatomical changes considerably outweigh typical day-to-day brain variability and measurement error. The mean cortical GMV values were nearly threefold higher than in controls. The mean GMV during gestation was sixfold (cortex) and threefold (MT) higher compared to the baseline variables. The CSF volume increase during pregnancy may result from increased water retention and cortical tissue compression. Postpartum alterations and regional differences in CT, GMV, and QA indicate cellular changes related to synaptic density, glial number, and myelination.

Conclusions

The study showed that pregnancy causes alterations in GMV, cortical thinning, and improved white matter microstructural integrity. These alterations correspond to serum estrogen hormone levels. Some alterations, such as GMV and CT decreases, continue after childbirth, but others, such as white matter integrity, appear temporary. The dataset offers a thorough brain map during gestation, offering an open-access resource for neuroscientists for further investigation.

The study's findings may help us better understand individual variations in parental behavior, sensitivity to mental health illnesses, and brain aging patterns. Future studies with demographically enriched populations could improve the universality of the findings. Further research could explore the variables that cause brain alterations during pregnancy and investigate the social and environmental determinants of maternal health.