We’ve all heard of pregnancy brain. Some of us have even experienced it first-hand. But what exactly is it, and why do we blame our mistakes on pregnancy?
Pregnancy brain - also known as baby brain or "momnesia" - refers to the forgetfulness, clumsiness, and difficulty concentrating that many women experience during pregnancy. But is the pregnancy brain just a myth, or is there real science behind it?
Let’s dive into the truth behind this phenomenon.
Pregnancy is one of the most profound biological experiences a person can go through. Despite this, we’ve known surprisingly little about how it affects the brain, until now. A groundbreaking study published in Nature has provided fascinating insights into how the human brain changes throughout pregnancy and into early motherhood.
For the first time, scientists have consistently tracked the structural changes of the brain that occur during pregnancy. MRI scans were used 26 times throughout a single participant's pregnancy: 4 scans before the pregnancy, 15 scans during, and 7 scans post-pregnancy, which were spread over the 2 years following childbirth.
Grey Matter Reduction
Across nearly all of the measured brain regions, the researchers identified a reduction in grey matter volume and cortical thickness. Grey matter is home to neural cell bodies and plays a key role in functions such as memory, sensory perception, and emotions, while cortical thickness correlates with cognitive abilities. These reductions occurred linearly over time, and while the reductions were followed by partial gains postpartum, they did not return to their previous baseline.
The idea that pregnancy shrinks parts of the brain might sound alarming. But in reality, these changes are an incredible example of the brain’s ability to adapt. It is suggested that these reductions are not random but are orchestrated to optimise maternal behaviours, as the brain regions most affected are those that have previously been linked to positive parenting behaviours.
“They found that cortical thickness and volume of grey matter decreased linearly across pregnancy in almost every region they measured. Decreases were followed by partial gains in the years after childbirth, but not a return to baseline levels.”
Increased White Matter Tract Integrity
At the same time that the researchers observed a reduction in grey matter, they found an increase in the integrity of white matter tracts (i.e., the nerve fibres that connect different paths of the brain), suggesting that these connections may have become more efficient during pregnancy. Unlike the changes in grey matter, which did not fully return to pre-pregnancy levels, the white matter tract integrity did. This inflection point was observed at childbirth, suggesting that these changes reverse in direction postpartum.
“The integrity of white-matter tracts increased throughout pregnancy and returned to baseline.”
Notably, some of the white matter pathways showing significant plasticity were those responsible for the communication between emotional and visual processing centres. This suggests that the brain is potentially adapting for improved maternal responsiveness.
“Areas that showed substantial white-matter neural plasticity included tracts that facilitate communication between emotional and visual processing hubs.”
So, now that we have learnt that the brain isn’t losing function during pregnancy but instead adapting to the demands of motherhood - what is causing pregnancy brain?
Simply put, anyone experiencing high levels of stress and sleep deprivation, such as new mothers, is bound to struggle with their memory and ability to focus - it is merely how the brain responds to exhaustion. The forgetfulness, often attributed to pregnancy, isn’t necessarily caused by pregnancy itself, but rather by the physical and emotional demands that come with it. In other words, it’s likely a correlation, not a direct cause.
Nonetheless, as we continue to uncover the fascinating ways the brain adapts to motherhood, one thing is clear: that maternal instinct is actually a remarkable example of the brain’s ability to evolve.
So next time someone jokes about pregnancy brain, remember: the brain isn’t failing - it's evolving.
Reference:
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
This article was written by Freya Wardell and edited by Julia Dabrowska, with graphics produced by Lilly Green. If you enjoyed this article, be the first to be notified about new posts by signing up to become a WiNUK member (top right of this page)! Interested in writing for WiNUK yourself? Contact us through the blog page and the editors will be in touch.
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