MRI images show exactly how a baby's head changes in the birth canal

Photo: Dr Olivier Ami - CHU Clermont Ferrand, France
Photo: Dr Olivier Ami - CHU Clermont Ferrand, France 

Imagine giving birth in the confines of an MRI scanner. That's exactly what seven incredible women did so that French researchers could obtain images of how a baby's head shape changes as it moves through the birth canal.

Called 'foetal head moulding', it's a necessary human adaptation in order for babies to pass through a human female's pelvis, which is much more complicated and risky for a baby's head to pass through than for other species'.

Lead researcher, gynaecologist Dr Olivier Ami of Auvergne University, analysed MRI scans before and during the second stage of labour. This is the stage where delivery of the baby takes place - the final stage is delivery of the placenta.

The analysis revealed that the plates in babies' heads move and overlap one another in order to mould the skull to the contours of the birth canal, meaning the head shape changes quite dramatically as the descent progresses.

Researchers now believe that a baby's head suffers much more stress that was previously thought, and that this accounts for the high rates (43 per cent for vaginal births) of brain and retinal bleeding.

Published in the journal PLOS ONE, 'Predibirth software was used to perform 3D vector reconstruction' which you can see below. The top row (purple) shows three angles of the baby's skull prior to birth, and the bottom row (red) shows the baby's skull plates moving as it is close to emerging from the birth canal.

Photo: Dr Olivier Ami - CHU Clermont Ferrand, France

Three-dimensional fetal brain MRI reconstruction before labor (shown in purple in A, C, E) and during the second stage of labor (shown in orange in B, D, F). Photo: Dr Olivier Ami - CHU Clermont Ferrand, France

Five of the seven newborns' heads returned to their pre-birth state, but for two of the babies, the changes were prolonged.

Two out of three babies with the most pronounced changes were delivered by emergency c-section, and the other after a 15 minute vaginal delivery..

Dr Olivier Ami - CHU Clermont Ferrand, France

Three-dimensional finite element reconstruction of the cranial bones before labor (A, C, E) and during the second stage of labor (B, D, F) in patient 5. Photo: Dr Olivier Ami - CHU Clermont Ferrand, France

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."

He also stressed the need for further research of a larger number of births to back up the recent findings.