The Maternal Brain and Neuroanatomical Changes During Pregnancy
Introduction
In 2022, a study conducted by Elseline Hoekzema et. al demonstrated that pregnancy changes the neural architecture and network organization primarily of the Default Mode Network in the brain, which primarily functions in memory consolidation, self-referential thought, mind-wandering, and autobiographical memory. These changes in the Default Mode Network were primarily influenced by the pregnancy hormone third-trimester estradiol, and interestingly other factors such as osmotic effects, stress, and sleep contributed no significant impact to the neurological connectivity within a mother’s brain.
Neuroplasticity and Maternal Behavior in Pregnancy
These anatomical findings also specifically correlated to maternal-fetal bonding, nesting behavior, and physiological responses to infant cues, demonstrating that the neurological changes that mothers undergo during pregnancy facilitate important maternal processes for connection with the infant. In this study, a cohort of women were followed from preconception to the late postpartum period and took part in four longitudinal experimental sessions involving a variety of technology to map the impact of pregnancy on the human brain. To examine the unique “pregnancy-related neuroplasticity”, a map of hormonal changes was collected based on biological samples and factors such as sleep and stress were taken into account. Hormone regulation supports reorganization of the central nervous system and thus drives neurogenesis and the transformation of other neural cells. Each individual’s post-pregnancy brain scan was compared with their pre-pregnancy brain scans, especially in relation to gray matter volume. This longitudinal data was also acquired from 40 nulliparous women (women who have never given birth). This study initially identified that there was no pre-existing difference between gray matter volume in primiparous women (women who have given birth only once) and nulliparous women. However, when investigating gray matter volume changes across sessions, and created subsequent post-hoc.
Mapping Neuroanatomical Changes During Pregnancy
In 2023, researchers Laura Pritschet et. al from the University of California explored the “neuroanatomical changes observed over the course of a human pregnancy”. Introducing the motivation for their research, they named that “the neural changes unfolding in the maternal brain throughout gestation have not been studied in humans”, though the physiological adaptations to support the fetus such as increase in metabolic and oxygen consumption have been previously thoroughly identified. These adaptations can still then be tied to their relative initiation by “hundred-to-thousand-fold” increases in the production of the hormones estrogen and progesterone, both of which contribute to a welcoming environment for the incoming fetus. Additionally, the study points out that a previous study’s observation in the reduction of gray matter after pregnancy, with traceable effects decades later, cannot properly acknowledge the process of change during gestation, or pregnancy, on the brain.
Mapping the first comprehensive “map” of the human brain throughout gestation, the California researchers used precision imaging to document the changes in a single individual from preconception, to two years postpartum, or after pregnancy. In addition to the previously acknowledged decrease in gray matter volume, the individual in the study displayed decreased cortical thickness. The researcher pronounces that this stands in contrast to the relative increase in the microstructural integrity of white matter, volume of the ventricle, and cerebrospinal fluid. The relationship between the former decrease and the latter increase is not yet known or described, if there is any correlation with hormonal or systematic redistribution of cellular functions in the brain of a gestating mother.
Limitations
As mentioned earlier, the study is only conducted on a single individual, that of a healthy 38 year old woman, who is primiparous, or has produced a child for the first time. The glaring limitation of this study is indeed its sample size of only one person; effective studies demonstrating breakthrough scientific effects tend to be done on many individuals over the course of several months or years. Additionally, while the primiparity of the subject is initially useful in the study of this emerging concept of brain change during pregnancy, it would be interesting to explore the effects of multiparous mothers of varying ages to observe how each pregnancy contributes to increasing changes to the brain and decrease in gray matter over time. The one question that particularly arises is: if these changes do build up over the course of multiple pregnancies, how do they affect neurological functions as a whole?
Significance
The gray matter makes up most of the outer layer of the brain, getting its tone from a high concentration of neurons. Neural proximity in the gray matter results in its importance for location of the processing of sensation, perception, voluntary movement, learning, speech, and more. Gray matter decline during pregnancy and postpartum, then, presents a significant challenge to the cognition of mothers, demonstrating a real inability to efficiently engage in the functions as described above that play a key role in human neurology.
References
Pritschet, L., Taylor, C.M., Cossio, D. et al. Neuroanatomical changes observed over the course of a human pregnancy. Nat Neurosci 27, 2253–2260 (2024). https://doi.org/10.1038/s41593-024-01741-0
Hoekzema, E., van Steenbergen, H., Straathof, M. et al. Mapping the effects of pregnancy on resting state brain activity, white matter microstructure, neural metabolite concentrations and grey matter architecture. Nat Commun 13, 6931 (2022). https://doi.org/10.1038/s41467-022-33884-8