Scientists have released fascinating 3D images which reveal exactly how a baby’s head is squashed during childbirth.
The changes occur during the second stage of labour, when the baby leaves the uterus and is pushed through the birth canal.
But, until now, the details of foetal head moulding remained unclear, and only one previous study had captured images of the process.
Now, MRI scans captured by French researchers reveal the huge stress that a baby’s skull goes through.
The baby’s head changes shape as it is pushed out by the mother, or when it is delivered by C-section.
Gynaecologists, led by Dr Olivier Ami of Auvergne University, used 3D MRI scans to capture detailed images.
Seven babies’ skulls and brains were scanned before and during the second stage of labour, the part where the baby is delivered.
The analysis, published in the journal PLOS One, revealed foetal head moulding during the second stage of labour in all seven babies, with different parts of the skull overlapping to varying degrees among the babies.
After birth, five of the newborns’ skull and brain shapes returned to their pre-birth state, but the changes persisted in two of the babies.
Two of the three babies with the greatest degree of foetal head moulding were delivered by emergency C-section.
In a C-section, the baby is pulled out of the womb through an incision in the mothers stomach that is around 10-20cm long.
A caesarean section is an operation where a doctor makes a cut in the abdomen and womb and lifts the baby out through it.
But the third was delivered vaginally within 15 minutes with minimal effort.
Overall, the researchers said that their findings suggest that babies experience greater skull stresses during birth than previously thought.
They said that potentially underlies the brain and retinal bleeding seen in many newborns after vaginal delivery, occurring in up to 43 per cent of vaginal births.
Study leader Dr Ami said: ‘During vaginal delivery, the foetal brain shape undergoes deformation to varying degrees depending on the degree of overlap of the skull bones.
‘Foetal skull moulding is no more visible in most newborns after birth.
‘Some skulls accept the deformation and allow an easy delivery, while others do not deform easily.
‘The fact that one of one of the children in our series showed the biggest deformation of its skull during the birthing process, was born easily after only a few maternal efforts, and showed signs of fetal distress despite continuous normal monitoring until the expulsion phase, raises the question of the relevance of our actual definition of a normal birth.’
He added that a larger study is needed to confirm their findings, but that their work shows the value of 3D MRI in capturing foetal head moulding.