3D MRI Images Show How a Baby's Head Shape Changes During Labor in Incredible Detail

baby's head delivery
An image showing how the bones in a baby's head shape during the second stage of labor in a patient who took part in the study. PLOS ONE

Scientists have mapped how the shape of a baby's head changes during childbirth to learn more about the process known as fetal head molding.

Compared with other mammals, the human pelvis is not shaped in a way that makes pushing out a baby's head particularly easy. In order to fit through the pelvis, the bones of a fetus's head can overlap or move closer to one another.

Scientists have long known this happens but they have only imaged it once before, according to the team behind the new study published in the journal PLOS ONE.

To find out more about fetal head molding, the scientists recruited seven pregnant women aged between 23 to 34-years-old, who were expected to have healthy vaginal births.

The team used techniques including 3D magnetic resonance imaging (MRI) to chart how the head a fetus's changes between pre-labor at 36 and 39 weeks and the second stage of labor, which starts when the cervix is dilated and ends in delivery. The scans were carried out while the women were resting and before she started pushing.

None of the babies had overlapping cranial bones in the womb. But the heads and brains of all seven fetuses changed to some degree during the second stage of labor. And in five of the babies, their heads had popped back into shape after they were born. This showed how flexible baby's heads are, the authors wrote.

baby's head womb
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). PLOS ONE

Of the total, five of the children were delivered vaginally, while two were delivered via emergency c-section as the baby's head was too big to fit through the woman's pelvis.

The findings, the authors argued, could one day be used to create a virtual labor which could pick up the potential risks of childbirth before the event.

baby head labour plos one
A reconstruction of how the bones in a baby's head changed during labor. Frontal bones are marked in pink, parietal bones in green, and the occipital bone in blue. PLOS ONE

Co-author Olivier Ami of Auvergne University in Clermont Ferrand Ami told Medical Express: "During vaginal delivery, the fetal brain shape undergoes deformation to varying degrees depending on the degree of overlap of the skull bones. Fetal skull molding is no more visible in most newborns after birth. Some skulls accept the deformation (compliance) and allow an easy delivery, while others do not deform easily (non-compliance)."

In most cases, a baby's head will even itself out. But if the head remains misshapen by the age of 6 months, a doctor may prescribe a helmet designed to relieve pressure and change the shape of the head.