In nearly 80% of the regions of Dr Chrastil’s brain, the volume of grey matter – tissue that controls movement, emotions and memory – decreased by about 4%, with only a small rebound after pregnancy.

But there were increases in white-matter integrity – a measure of the health and quality of connections between brain regions – in the first and second trimesters, which returned to normal levels soon after birth.

The changes are similar to those during puberty, the researchers say.

Studies in rodents suggest they could make mothers-to-be more sensitive to smells and prone to grooming and nesting, or homemaking.

“But humans are way more complicated,” Dr Chrastil says.

She did not personally experience any “mommy brain” during her pregnancy but was certainly more tired and emotional in the third trimester, she says.

The next step is to collect detailed brain images from 10 to 20 women and data from a much larger sample at particular timepoints, to capture a wide range of different experiences.

In this way, Dr Chrastil says, “we can determine whether any of these changes could help predict things like postpartum depression or understand how something like pre-eclampsia could affect the brain”.