Pregnancy reshapes the brain in quite dramatic ways. In fact, we can tell if someone has been pregnant by looking at their brain structure.
There are changes in the brain’s grey matter volume. These are in regions that control complex thinking, mood and “social cognition”, or our ability to understand the needs and wants of others.
These changes are long-lasting. They’ve been detected in women six years after birth. Large-scale population studies have even shown this grey matter signature of pregnancy decades later.
More recently, a remarkable study scanned one woman 26 times from before conception through to two years after birth, to map these changes as they actually unfolded.
The researchers watched the volume of her grey matter decline across the pregnancy. The outer layer of her brain, the cortex, also got thinner. These changes were a response to the enormous rise in pregnancy hormones, and the brain changes tracked these hormone surges closely.
At the same time, her brain’s white matter, the wiring that connects different brain regions, was strengthened during pregnancy. This means brain signals can travel faster and more efficiently. This strengthening occurred during the first and second trimesters before settling back to pre-pregnancy levels after birth.
It might sound alarming that the brain loses grey matter during pregnancy, but this is almost certainly not damage.
Instead, scientists think this reflects a kind of fine-tuning, with the brain preparing itself for the demands of motherhood. This is in a similar way to the adolescent brain reorganising itself during puberty.
So far from breaking down, mothers’ brains appear to be purposefully remodelling.
If the brain is undergoing such substantial structural change, you might expect problems to show up when we test how new mothers actually think – but mostly, we don’t see such problems.
The largest study of its kind, published recently by Australian and US scientists, measured memory, thinking and processing speed in 150 new mums and 150 new dads. They then compared them to women and men who did not have children.
New parents performed just as well as everyone else, with no sign that becoming a parent impaired memory or thinking. These skills also didn’t worsen or improve over time, with similar performance over the first two years of being a new parent.
This comprehensive study is the latest to confirm a mismatch between what mothers report experiencing and what we see on objective tests.
Some studies do find subtle changes, particularly in memory during pregnancy itself. But the effects are small and inconsistent, and rarely match the experiences mothers describe.
The brain changes are real and lasting. The memory and attention decline is likely mostly fiction, or at least, far less of a culprit than the stereotype suggests.