You walk into the kitchen and forget why you’re there. You put the milk in the pantry and the keys in the fridge. You lose your train of thought halfway through a sentence.
If you’ve recently had a baby, you might blame all this on “baby brain” – that foggy, forgetful feeling so many new mothers describe.
But is “baby brain” real? Does the brain really change during pregnancy? And if so, how’s all this related to how new mothers think?
Yes, pregnancy can reshape the brain
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.
But how does this actually affect mothers?
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.
What’s really going on?
So what actually causes baby brain? We don’t fully know. But the evidence leads us away from pronounced shifts in brain function and towards the circumstances of new parenthood.
The most obvious culprit is sleep. New parents are chronically sleep-deprived, and we know sleep loss alone degrades attention, working memory and processing speed.
Tellingly, the Australian-US study found fathers (who don’t undergo pregnancy’s hormonal upheaval) showed subtle memory and thinking effects too. The researchers linked this to lack of sleep.
Then there’s the “cognitive load” of a new baby. There are so many things for a new parent to think about – including tracking feeds, sleep schedules and nappy changes – while adjusting to their new life.
So forgetting why you walked into the kitchen may say less about your memory than about the fact that your mind is holding far too much at once.
Stress, anxiety and the emotional intensity of early parenthood can all chip away at the kind of focused attention that makes us feel alert and in the moment.
So, fact or fiction?
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.
The fog new parents feel is real, but it seems to be driven less by motherhood rewiring the brain than by exhaustion, overload and the relentless demands of caring for a tiny human.
