"Station" as part of the physical exam in pregnancy
"What Does "0" Station Mean In Childbirth?
The whole mechanism of delivering a child, of course, involves the actual exit of the baby through the mother's pelvis. A traditional reference has developed through generations of obstetricians. This reference, called "station," is used to document on the record how far down the head of the baby has descended toward delivery. In discussing a laboring situation, nurses and doctors must be able to convey information that can be understood universally among them.
The station is based on how far down the head has dropped in relation to two bony prominences (called the ischial spines) that mark the midpelvis (halfway out). In a pelvic exam, the examiner can feel where these spines are, protruding from the pelvic sidewalls. Then, the position of the "presenting part," i.e., that part of the baby (hopefully, the top of the head) that will be the first to deliver, is felt as compared to the ischial spines. If the very top of the head is at the ischial spines, it's called a zero station. And for every centimeter distance from the spines, either above or below, the presenting part can be said to be anywhere between -3 and +3.
"-3" is 3 cm. above the ischial spines. +3 is 3 cm below the ischial spines, and, well, you better call the doctor, because that baby's about to deliver! True, a +3 station shows the baby's scalp on the perineum (at the opening of the vagina).
Friedman's Curve, which is a graph used to note progress of labor, plots two different things, the station and the cervical dilatation. With normal labors progressing to delivery, the station starts at the upper left and over time is marked toward the lower right of the graph; while the dilatation begins at 0 at the lower left and rises to 10 over time at the upper right hand corner of the graph. In this way, there should be an "X" on the graph. Any distortion of this X will indicate either a problem in the descent of the baby's head or in the dilatation, and such graphical distortions are used to legitimately justify a C-section when vaginal delivery proves impossible. This is called "Failure to Progress."
Usually when the baby "drops" during the third trimester of pregnancy, this signifies the attainment of a 0-station. This is a good sign for pending delivery.