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Recent scientific studies have revealed the intricate bidirectional relationship between female sex hormones and the human brain. The brain is not only a significant source of estrogens, but natural occurring fluctuations of estrogens and progesterone during the menstrual cycle and during menopause (discussed in previous newsletter articles) have been shown to have major effects on structure and function of the brain, consistent with the behavioral and emotional changes associated with these periods in a woman’s life.

“…the neural changes unfolding in the maternal brain throughout pregnancy in humans are poorly understood.”

Pregnancy is a period of profound hormonal and physiological changes experienced by millions of women annually, yet the neural changes unfolding in the maternal brain throughout pregnancy in humans are poorly understood. Worldwide, nearly 85% of women experience one or more pregnancies in their lifetime, with 140 million women becoming pregnant each year.

Over an approximately 40-week of pregnancy, the maternal body undergoes profound physiological adaptations to support the development of the fetus, including increases in plasma volume, metabolic rate, oxygen consumption and immune regulation. These rapid adaptations are initiated by 100-fold to 1,000-fold increases in hormone production, including estrogen and progesterone.

While many of the bodily changes in response to this dramatic increase in female sex hormones have been studied in detail, the significant reorganization of the brain and their behavioral consequences are poorly understood. Evidence from studies in animals and in humans has identified pregnancy as a period of remarkable neuroplasticity.

Neuroplasticity is the ability of neural networks in the brain to change through growth and reorganization. It is when the brain is rewired to function in some way that differs from how it previously functioned. This remodeling of different cells in the brain (including dendritic spine growth, microglial proliferation, myelination and astrocyte remodeling) are driven by pregnancy related increases in sex hormone synthesis and are most pronounced in brain regions that promote maternal behavior.

“While several studies have looked at long lasting brain changes after delivery, changes that occur within the maternal brain during pregnancy itself are largely unknown.”

While several studies have looked at long lasting brain changes after delivery, changes that occur within the maternal brain during pregnancy itself are largely unknown. Even though findings from a recent study suggest that pregnancy is a highly dynamic period for neural remodeling, a detailed map of how the human brain changes throughout the gestational period does not exist.

“This…allowed them to document the precise timing and magnitude of brain alterations during and after pregnancy.”

In a study by Laura Pritschet and colleagues from the Department of Psychological & Brain Sciences, University of California, Santa Barbara and published in the journal Nature Neuroscience in September 2024, scientists have captured a woman’s cognitive evolution into motherhood, taking repeated brain scans over three years to reveal the most detailed picture yet of the dynamic brain changes that unfold over the course of pregnancy.

Laura Pritschet, a postdoctoral fellow in psychiatry at the University of Pennsylvania Perelman School of Medicine, had previously put herself in the scanner every day for a month during her menstrual cycle, revealing that brain networks are reshaped over the course of a month. When one of the research team members, Elizabeth R. Chrastil, planned to get pregnant, she didn’t want to miss the opportunity to study herself.

With a team of collaborators she went into the scanner 26 times — before, during and after her pregnancy — providing an unprecedented view of a transformative event in human biology that has long been overlooked by science. This process allowed them to document the precise timing and magnitude of brain alterations during and after pregnancy. The main findings of this remarkable study are summarized below:

• A reduction in Gray Matter Volume and Cortical Thickness: The study observed a noticeable reduction in gray matter and cortical thickness throughout the brain, with decreases seen in 80% of the regions examined. Grey matter is made up of large number of nerve cells and their extensions. The observed increase in cerebrospinal fluid volumes may have contributed to apparent reductions in cortical thickness by compressing brain tissue. The authors speculated that these reductions, especially in areas involved in social cognition, may prepare the brain for the demands of motherhood by potentially enhancing the mother’s sensitivity to infant cues.
• An Increase in White Matter Integrity: Unlike gray matter, white matter in the brain showed increased structural integrity during pregnancy. White matter is made up of a large network of nerve fibers in the brain that allows the exchange of information and communication between different areas of your brain. This enhancement could support the brain’s connectivity and communication, likely aiding in the development of new behavioral adaptations required for parenting. White matter changes peaked during pregnancy but returned to baseline shortly after childbirth. This pattern contrasts with gray matter changes, which showed only partial recovery after delivery.
• Hormonal Influences: The changes in brain structure appeared closely linked to fluctuations in estradiol and progesterone, which increased significantly during gestation and dropped after childbirth. These hormones are thought to drive the observed brain adaptations, highlighting pregnancy as a unique period of neuroplasticity, the brain’s ability to reorganize and form new connections.
• Long-Lasting Brain Changes: Some changes, like the reduction in gray matter, persisted two years after childbirth, suggesting long-term alterations in the brain due to pregnancy. These enduring changes might be essential for sustained maternal behaviors.

“…neuroscientists are just beginning to document how hormones drive an intricate, choreographed set of changes that may prepare and hone the brain for parenting.”

This research offers a foundational map of how the brain adapts during pregnancy, advancing our understanding of maternal brain changes and providing a valuable resource for studying the neurological underpinnings of motherhood. The emerging evidence suggests that “mommy brain” could be a real thing, but nothing like the pop culture conception of young mothers becoming cognitively fuzzy and absent-minded. Instead, neuroscientists are just beginning to document how hormones drive an intricate, choreographed set of changes that may prepare and hone the brain for parenting.