There are many situations in which the use of obstetric forceps may help delivery. As a result, there are over 600 different types of forceps, of which maybe 15 to 20 are currently available. Most hospitals have on hand between five and eight different types of forceps. While each type of forceps has been developed for a specific delivery situation, all forceps share several design characteristics.
All forceps consist of two branches that are maneuvered into position around the baby's head. These branches are defined as left and right on the basis of the side of the mother's pelvis to which they will be applied. The branches usually, but not always, cross at a midpoint called the articulation. Most forceps have a locking mechanism at the articulation, but a few have a sliding mechanism allowing the two branches to slide along each other. For deliveries where little or no rotation is required (the baby's head is in line with the mother's pelvis), forceps with a fixed lock mechanism are used; for deliveries requiring some rotation, forceps with a sliding lock mechanism are used.
All forceps have handles; the handles are connected to the blades by shanks of variable lengths. If a forceps rotation is being considered, a forceps with longer shanks is used. The blade of each forceps branch is the curved portion is used to grasp the baby's head. The blade characteristically has two curves, the cephalic and the pelvic curves.
The cephalic curve is shaped to conform to the baby's head. Some forceps have a more rounded cephalic curve and others have a more elongated curve; the type of forceps used depends on the shape of the baby's head. The forceps should surround the baby's head firmly, but not tightly.
Forceps with a more rounded curve are usually referred to as Elliot forceps. Elliott-type forceps are used most often in women who have had at least one previous vaginal delivery; this is because the muscles and ligaments of the birth canal provide less resistance during second and subsequent deliveries, allowing the baby's head to remain rounder.
Forceps with a more elongated cephalic curve are used when the baby's head has changed shape (becoming more elongated) as it moves through the mother's pelvis. This change in the shape of the baby's head is called molding and is much more prominent in women having their first vaginal delivery. The type of forceps used most often in this situation is the Simpson forceps.
The pelvic curve of the forceps is shaped to conform to the birth canal. This curve helps direct the force of the traction under the pubic bone then outward and upward. Forceps used for rotation of the baby's head should have almost no pelvic curve. The Kielland forceps are probably the most common forceps used for rotation; they also have a sliding mechanism that can be helpful when the baby's head isn't in line with the mother's pelvis (asynclitism). On the other hand, Kielland forceps do not provide much traction because they have almost no pelvic curve.
The position of the birthing woman is important in the preparation for forceps delivery. The mother's buttocks should be at the edge of the bed or table and the thighs should be up and out, but not overly stretched. This position helps to minimize the likelihood of inadvertent injury to the mother's back, hips, legs, and perineum. If the mother's hips are not in the optimal position, her perineum can be directly in the way of the baby's descending head, thus increasing the risk of injury to the perineum and/or extension of an episiotomy. Leg holders are generally the best way to support the mother's legs. The mother's bladder is usually emptied with a catheter, especially when forceps other than outlet forceps is being considered. This can prevent potential bladder injury.
After the decision to use forceps has been made, guidelines regarding their usage must be followed. There are guidelines regarding inserting and applying the forceps (that is, getting the forceps to where they need to be alongside the baby's head) and guidelines regarding use of the forceps to perform traction or rotation.
Applying the Forceps
The way the forceps are applied depends on the position and station of the baby's head, the specific type of forceps to be used, and the experience and training of the provider.
In occiput anterior positions (baby facing down) the forceps blades should slide easily into place along the doctor's hand that is in the vagina. Usually the left blade is inserted first (the left blade is defined as the blade that goes between the baby's head and the left side of the mother's pelvis). The right blade is then inserted in the same fashion and the lock of the two blades should come together easily. Each blade should be about a finger's width below the posterior fontanelle (the "soft spot" in the back of the baby's head between the unfused cranial bones). When properly applied to a baby in occiput anterior position, the blades will extend in front of the baby's ears and on to the cheeks.
When the baby is in occiput posterior presentation (facing up), the blades can be applied in the same fashion as for an occiput anterior (facing down) presentation. The tips of the blades still rest on the baby's cheeks, but in this position the blades meet just below the anterior fontanelle. When the baby's head is in a transverse position (facing the side of the pelvis), the back blade is inserted first to help stabilize the position of the baby's head.
Once the forceps have been applied, it is important for the doctor to make sure they are properly positioned on the baby's head. If the forceps application is not easy or requires force, then something isn't right. Commonly, this means that the station is not as low as expected or that the position of the head has been incorrectly assessed. It may also mean that the wrong type of forceps is being used. If the forceps don't go on easily, they shouldn't be forced.
Rotation and Traction
Once properly applied, obstetric forceps can be used for rotation of the baby's head and for traction for delivery of the head.
An outlet forceps delivery may be performed when the baby's head is visible at the vaginal opening and is within 45 degrees of an occiput anterior or an occiput posterior presentation. As the baby's head is rotated, traction is usually simultaneously performed.
Rotations greater than 45 degrees can safely be performed with forceps, but are associated with a greater potential for complications. Larger rotations often require that the baby's station be shifted further up or further down the birth canal. It is important that a very skilled and experienced provider perform any of these more complicated maneuvers. A doctor that has experience in manipulation of the forceps can utilize the pelvic curve in the safest and most successful way possible.
Forceps are most often used to apply traction to guide the baby down and out through the birth canal. Traction should be directed along the axis of the birth canal-that is, behind and under the pubic bone. With occiput anterior presentations, this will often result in the handles of the forceps being directed downward and then upward as the back of the baby's head comes under the pubic bone. When a baby is being delivered in the occiput posterior position, the traction will need to be directed downward.
Traction should be applied in association with contractions and pushing efforts, with rest periods in between. It is important to avoid undue pressure on the baby's head; the doctor does this by loosening the handles in between contractions.
Some providers will remove the forceps before the baby is delivered and allow the head to deliver spontaneously; others will remove the forceps after the baby's head is delivered. There is no evidence proving that one approach is better than the other. The decision, therefore, often depends on the potential urgency of delivery. As with all deliveries, the condition of the baby should be assessed immediately after delivery.