Which presentation involves the fetal head being extended or hyperextended?

The presentation that involves the fetal head being extended or hyperextended is the frank breech presentation. In this position, the fetal buttocks are presenting first while the legs are extended along the body with the feet near the head. This results in the back of the fetal head being presented at the pelvic inlet, leading to an extension or hyperextension of the neck as the fetus tries to navigate through the birth canal.

This hyperextended position contrasts with other types of breech presentations where the fetal head is usually not in an extended position relative to the body. For instance, in a complete breech presentation, the fetal knees are flexed, and the feet are positioned near the buttocks. In a double footling breech, one or both feet precede the buttocks, leading to different alignment of the fetal head. In an incomplete breech, one limb is extended while the other is flexed, which also does not involve hyperextension of the head.

Thus, the frank breech configuration specifically leads to the characteristic hyperextension of the fetal head as it is positioned at the maternal pelvis.