Position of the Fetus
The position of the baby's head changes during the course of labor. At the onset of labor, the baby is usually facing toward the mother's right hip with the back of the head toward the mother's left hip. This position is called left occiput transverse. This position allows the widest part of the baby's head (the front-to-back axis) to correspond with the widest part of the mothers upper pelvis (side-to-side).
As labor progresses and the baby descends into the mother's pelvis, the baby's head encounters the lower part of the mother's bony pelvis and pelvic floor. Since the widest part of these structures runs from front-to-back, the baby's head normally rotates so that the back of the head is directly below the mother's bladder and the baby's face is directed toward the mother's tailbone. This position is called occiput anterior. A position halfway between left occiput transverse (back of the baby's head toward the mother's left side) and occiput anterior (the back of the baby's head toward the front of the mother) is called left occiput anterior. In this position the back of the baby's head is at a 45 degree angle to the left of the midline.
Station of the Fetus
Station refers to how far down the baby's head has descended into the mother's pelvis. The birth canal is shaped like a cone, curving underneath and behind the pubic bone. Its narrowest section lies between two bony landmarks of the pelvis (one on either side), called the ischial spines. The geometric plane that extends through these spines and up to the pubic bone is called the midpelvis and is arbitrarily described as zero station. As the baby's head descends below this plane, the station of the baby is indicated by a number representing how many centimeters the baby has descended. For example, the baby is said to be at a +2 station when the head is two centimeters below the plane defined by the ischial spines and the pubic bone. When the baby's head is at zero station, the largest part of the head has entered the bony pelvis. Until the baby's head is at least at zero station, the baby hasn't completely entered the pelvis. When the baby's head is above zero station it is said to be unengaged. Forceps deliveries should never be attempted when the baby is unengaged. In the past, forceps delivery of an unengaged baby was called a high forceps. Forceps deliveries at less than +2 station are termed midforceps and can also be quite tricky.