Clock approach to fetal head position on ultrasound

On ultrasound, the landmarks for determining fetal head positions are the fetal orbits, the midline cerebral echo, and the occiput. The fetal head position can be described by the position of these landmarks with respect to the hour hand on the face of an analog clock. For example, occiput positions from 3:30 to 8:30 are OP, occiput positions from 9:30 to 2:30 are OA, and occiput positions at the remaining one hour segments 2:30 to 3:30 and 8:30 to 9:30 are OT (left versus right depends on the position of the orbits: Orbits on the maternal right = LOT, orbits on the maternal left = ROT).