Feel sorry for mothers. Not only is the cost of having a child simply extortionate, but the human pelvis is not particularly well-adapted for the actual process of giving birth to large-headed newborns.

One of the ways humans have evolved to get around this narrow-pelvis, big-head dilemma is with a soft, moldable skull that fuses and hardens at some point between seven and 18 months. This squishy skull can shapeshift under pressure, allowing it to squeeze through the birth canal.

Now, scientists have used 3D scanning to demonstrate how the fetal brain changes shape during the delivery process. The results have been published in the journal PLOS ONE.  

Twenty-seven pregnant women were scanned with an MRI machine between 36 and 39 weeks of gestation. Seven of these women were then scanned again, no more than 10 minutes before giving birth. 

The resulting images show varying degrees of what they call "fetal head molding", revealing clear differences between the first and second set of images. While not one of the 27 images in the first set showed overlapping fetal structures, all seven in the second set did – demonstrating the way the brain shape changes during labor to fit through the birth canal.

Right after birth, this "cranial deformity" was no longer visible in five out of the seven babies. The parameters of their skulls were "identical" to what they had been when in the womb. 

As for the three newborns with the most noticeable molding of the skull (and the most severe brain shape deformations), two were born by c-section and one was born via natural birth.

In 2017, photographer Kayla Reeder captured some incredible images of a baby Graham, whose sideways positioning resulted in extreme molding of the skull. But don't worry – in this instance, the baby's head formed back into a normal shape, highlighting just how complex (and flexible) the human body really is.