Author: Magdalena Martínez García, Neuroscience Ph.D student, Neuroimaging group, Instituto de Investigación Sanitaria Gregorio Marañón of Madrid | Editors: Negin Nia and Arrthy Thayaparan (Blog Coordinators)
Published: February 11th, 2022
Pregnancy is one of the most profound physiological transitions a woman experiences in her lifetime, one that affects every aspect of her body. A cascade of hormonal events coordinates substantial changes in the cardiovascular, respiratory, renal, and muscular systems of pregnant mothers, to name a few affected systems. These extreme physiological changes guarantee successful fetus development, labour, and lactation, but at the same time also leave a mark in the mother’s brain. Until recently, neuroscience research has largely ignored how the brain responds to female hormonal transitions, such as pregnancy. Luckily, this scenario is rapidly changing as more research is focusing on understanding the human maternal brain.
The maternal brain through the lens of neuroimaging
Neuroimaging studies conducted over the last decade have shown that the transition to motherhood is associated with major structural brain changes visible by Magnetic Resonance Imaging (MRI). However, the precise evolution, as well as the nature of such changes, are still open questions. There might be a simple explanation for this gap of knowledge: recruiting and scanning mothers during pregnancy or after childbirth is a delicate process. Most studies tracking the human maternal brain have restricted neuroimaging sessions to two-time points, mainly during the postpartum (or the first months after birth), so researchers have not yet been able to reliably explain how the brain changes its structure during pregnancy.
An easier way to describe the evolution of a mother's brain anatomy during and after pregnancy could be to unify the results of different longitudinal studies. A pilot brain trajectory could then be developed based on these results. This task is feasible given that existing studies have captured slightly different periods during the motherhood transition from conception to several years after giving birth. As part of a recent review article published in Frontiers of Global Women's Health, I aimed to put this puzzle together by combining findings from the studies that have tracked mothers' brain anatomy so far.
Maternal brain changes are not linear but dynamic
After integrating the results, one thing became evident: a mother's brain does not undergo uniform or continuous changes. Brain regions associated with empathizing, emotion regulation, and reward-seeking show distinct stages of growth and shrinkage during pregnancy, early postpartum, and late postpartum (Figure 1). For instance, while studies that scanned mothers before conceiving and then again during the postpartum suggest a decrease in brain volume and a flattening of the cortex induced by pregnancy, studies conducted after childbirth reveal brain volume increases in the immediate postpartum (a few days to one month postpartum), early postpartum (several weeks to four months postpartum) and intermediate postpartum (two to five months postpartum).
Scientists from the NeuroMaternal, BeMother and Pregnancy and the Brain laboratories even found that most brain volume changes persisted six years after childbirth in a subsample of mothers of the original study.
A topic raising more questions than answers
In short, the effects of pregnancy on a woman’s brain are profound and dynamic, but more research is needed to truly understand the women’s brain adaptations during healthy pregnancies. For instance, we don't have solid evidence on when exactly maternal brain changes begin during pregnancy. So far, it is just as likely that the volume of the brain decreases steadily or that it decreases abruptly close to delivery. Likewise, the postpartum time at which brain volume increases reaches its maximum has yet to be determined.
Another important unresolved question is the neural mechanisms that operate in the human maternal brain. Scholars are prone to regard the brain changes observed in mothers as signs of neuroplasticity, which refers to the brain's ability to change and adapt through modifications in the number and shape of the neurons, glia, and synapses. Experiments with rodents have established several neuroplastic events occurring during pregnancy and postpartum periods. But unfortunately, Magnetic Resonance (the technique that gives the highest definition of the human brain), does not have enough resolution to detect the cellular level and thus can't detect neuroplastic processes. Neuroimaging advances that increase the anatomical resolution of the images and better determine the microstructural tissue properties will provide exciting new details on the neural mechanisms behind the macroscopic brain changes observed in mothers.
The answers to all these questions are crucial to establish when the brain is most susceptible to developing mental illnesses. One in five birthing mothers suffers from postpartum depression and in extreme cases psychosis towards the newborn. Despite the importance of early detection of postpartum depression, science still lacks the means for timely diagnosis and treatment of this and other perinatal mental disorders. By identifying how healthy mothers’ brains adapt, we will gain insight into how these adaptations can sometimes deviate and lead to perinatal mental disorders.
European scientists are leading the way in understanding how women' brains adapt to motherhood
For researchers to be able to produce reliable brain trajectories, it is crucial to scan participants multiple times during pregnancy and postpartum and to use multimodal techniques that can provide a comprehensive non-invasive histological picture of the brain. Neuromaternal, led by Dr. Susanna Carmona, BeMother, led by Dr. Oscar Vilarroya, and Pregnancy and the Brain, led by Dr. Elseline Hoekzema, are three of the most highly regarded neuroimaging centers in Europe that are currently dedicated to investigating the brain trajectories of pregnant mothers through large-scale longitudinal studies. We can’t wait to find out what they discover next.