An indication of how far the presenting part of the baby (usually the head) has progressed through the pelvis. A baby who has just begun to descend may be at -4 or -5 station. A fully engaged baby (one whose head has reached the bony landmarks of the pelvis) is said to be at "zero (or 0) station". As the head continues to descend through the pelvis, it is considered +1 or +2 station until it crowns at the vaginal opening at +5 station.