Descent

The term fetal descent is used to describe the progressive downward movement of the fetal presenting part (commonly the head) through the pelvis. When there is regular and strong uterine contraction, and the size of the babys' head and the size of the mother's pelvic cavity are in proportion so the baby can pass through, there will be continuous fetal descent deep into the pelvic cavity. Since the pelvic cavity is enclosed with pelvic bones, when the uterus is strongly pushing down, occasionally the fetal scalp bones undergo overlapping at the suture lines in order to allow the head to pass through the narrow space. This overlapping is called moulding. The commonest types of moulding include one parietal bone overlapping over the other parietal bone along the sagittal suture (Figure 1.4), the occipital bone overlapping the temporal bone, and the frontal bone overlapping the parietal bones.