The experience often called “pregnancy brain” or “momnesia” is a common phenomenon reported by many expectant and new mothers. It describes a collection of cognitive changes, such as memory lapses, difficulty concentrating, or feeling mentally “foggy.” Scientific research is beginning to uncover the biological reasons behind these cognitive shifts during pregnancy. This article explores how pregnancy impacts the brain.
Understanding Brain Changes During Pregnancy
Neuroimaging techniques like MRI scans indicate that the brain undergoes alterations during pregnancy. Studies have shown changes in both grey matter and white matter volume and integrity. Grey matter, involved in processing information, thinking, learning, and memory, has been observed to decrease in volume in certain brain regions during pregnancy. This reduction can affect areas linked to social cognition, emotional processing, and decision-making.
This reduction in grey matter is often described as a “fine-tuning” or “pruning” of neural circuits rather than a detrimental shrinkage, similar to changes seen during puberty where the brain becomes more specialized. Research tracking brain changes throughout pregnancy has revealed that total grey matter volume and cortical thickness can decrease, with a partial rebound after birth. These changes are significantly larger than the natural variability seen in non-pregnant individuals.
In contrast to grey matter, some studies have identified increases in white matter integrity during pregnancy, particularly in the first two trimesters. White matter consists of nerve fiber tracts that facilitate communication between different brain regions. This temporary strengthening of white matter suggests enhanced efficiency in information transfer within the brain during pregnancy.
What Causes These Brain Changes?
The primary drivers of brain changes during pregnancy are significant fluctuations in hormone levels. Hormones such as estrogen, progesterone, and oxytocin influence brain structure and function. Estrogen levels, for instance, rise dramatically during pregnancy and then decline sharply after childbirth. This surge and subsequent drop in estrogen are thought to affect neural activity and may contribute to memory and attention changes, particularly impacting the hippocampus, a brain region sensitive to hormonal shifts and involved in memory.
Progesterone, another hormone that increases during pregnancy, has been noted for its calming effect on the brain and its role in managing mood and reducing anxiety. It also contributes to the bonding process between mother and baby. Oxytocin, often referred to as the “love hormone,” is released during skin-to-skin contact and breastfeeding, fostering emotional connections and promoting feelings of attachment. The sequential release of these hormones reorganizes the female brain, preparing the future mother for offspring care.
Beyond hormonal influences, other factors can contribute to cognitive symptoms experienced during pregnancy. Sleep deprivation is common due to physical discomfort or frequent urination, and it is known to impair memory and concentration in all individuals. The increased stress and profound psychological adjustments involved in preparing for motherhood can also contribute to feelings of mental overload and difficulty concentrating. However, the physiological and hormonal shifts remain the primary drivers of the structural brain alterations.
How Pregnancy Brain Impacts Daily Life
“Pregnancy brain” manifests in daily life through various cognitive symptoms. These can include increased forgetfulness, such as misplacing keys or forgetting appointments, and difficulty with multitasking. Reduced attention span and a general feeling of being “foggy” are also commonly described. Around 50% to 80% of pregnant individuals report experiencing these cognitive shifts.
There is an emerging scientific theory that some of these brain changes may serve an adaptive purpose, enhancing the brain’s capacity for maternal caregiving. The reduction in grey matter, particularly in areas related to social cognition, is thought to streamline neural pathways, potentially making the brain more efficient in processing social interactions and interpreting emotional cues. This “pruning for efficiency” may sharpen a mother’s ability to detect and respond to her infant’s needs, such as decoding cries or facial expressions, thereby strengthening the parent-child bond.
These neural shifts are believed to heighten responsiveness to infant cues and prepare the brain for the demands of childcare. The adaptations are thought to improve emotional regulation, social interactions, and attachment, skills beneficial for nurturing a newborn. While some studies have shown slight decreases in cognitive performance on memory tests, these effects are subtle and more noticeable to the pregnant person than to others.
How Long Do These Changes Last?
Research findings regarding the duration of brain changes and associated cognitive symptoms vary, but suggest a period of recovery. Structural brain changes, such as the reduction in grey matter volume, may persist for at least two years postpartum, with some studies indicating they can last even longer. However, there is evidence of partial recovery in grey matter volume during the postpartum period, with increases observed from late pregnancy to six months postpartum.
While structural changes can be long-lasting, the cognitive symptoms associated with “pregnancy brain” improve within months after birth. The brain exhibits neuroplasticity, its capacity to adapt and reorganize. This plasticity allows for changes during pregnancy to support the transition to motherhood and for subsequent recovery and reorganization in the postpartum period. For example, brain regions associated with maternal behavior, such as the amygdala and prefrontal cortex, may show increases in grey matter volume in the initial weeks postpartum.