How do skull bones move during a baby's birth through the pelvis?

During a baby's birth, the bones of the skull do not move independently in the way joints typically function; rather, the skull undergoes a process called molding to adapt to the mother's pelvis.12

This molding is made possible by fontanels—soft spots covered by tough, fibrous membranes located at the junctions of the cranial bones—and the fact that the sutures (joints) between these bones are loose in infants. These features allow the skull bones to shift slightly and overlap, which reduces the circumference of the fetal head as it passes through the birth canal.132

As the head descends, uterine contractions and the resistance of the pelvic floor force the head into a flexed position, further optimizing its shape for passage. These structural adaptations are essential for the safe delivery of the infant, as they allow the cranium to accommodate the pressures exerted during labor.21