Which landmark of the fetal head is used to determine station in well-flexed cephalic presentation?

In a well-flexed cephalic presentation, the occipital bone is the pivotal landmark used to determine the station of the fetal head during labor. The station refers to the position of the presenting part of the fetus in relation to the ischial spines of the mother's pelvis, and it is expressed in centimeters either above or below these spines.

In a scenario where the fetus is well-flexed, the chin is tucked towards the chest, and the occiput presents to the pelvic inlet. This positioning makes the occipital bone the leading part of the fetal head, allowing for a clear reference point to assess descent during labor. As the labor progresses, the station changes as the occipital bone moves downwards through the pelvic canal.

Other structures, such as the frontal, parietal, and temporal bones, do not provide the same level of reference for determining station because they are either positioned more posteriorly or are not the presenting part in a typical well-flexed cephalic presentation. Thus, the occipital bone is the most reliable anatomical landmark for this assessment.