Operative vaginal delivery, in this case, forceps delivery, may be considered when the prerequisites have been fulfilled (see the following section, Prerequisites) and there is a valid reason. Reasons to perform an operative vaginal delivery can be related to situations in the baby or the mother. Operative vaginal delivery is an option when the baby shows signs of abnormal heart rate.
Other indications include compression of the umbilical cord, premature separation of the placenta, failure to progress in the second stage of labor, or when the second stage of labor should be shortened because of a medical condition.
The second stage of labor refers to the time interval between complete dilation of the cervix and delivery of the baby. The average duration of the second stage of labor (without an epidural) is one to one-and-a-half hours with delivery of a first baby and considerably shorter with subsequent deliveries (averaging 20 to 30 minutes). As the second stage of labor extends beyond these time frames, women (and their support persons) should discuss the risks and benefits of continued labor versus operative delivery with their doctor. Prolongation of the second stage of labor may be the result of true cephalopelvic disproportion (when the baby's head is too big or the pelvis is too small) but more often represent a combination of inadequate contractions, excessive analgesia, maternal exhaustion, or lack of cooperation. Besides consideration of operative delivery, consideration should be given to the options for correcting any of these other causes of a prolonged second stage of labor.
When the cervix is completely dilated and the baby's head is descending through the pelvis, each contraction is associated with a strong urge to bear down and push the baby out (unless the mother has received excessive anesthesia). For the overwhelming majority of women, this bearing down effort causes no specific problems. However, a few women with certain medical conditions may encounter serious problems with pushing during the second stage of labor. Some of the conditions that require special consideration include certain types of heart disease-particularly stenosis (or narrowing) of heart valves, intrinsic disease of the heart muscle, and hypertension in the lung arteries. In addition, women with identified but unrepaired blood vessel malformations in their brain (called aneurysms or arteriovenous malformations) should also minimize the amount of pushing they do in the second stage of labor to reduce the risk of brain hemorrhage during delivery. Other medical problems that can affect women of reproductive age, such as certain neuromuscular or respiratory diseases, may impair the ability to push effectively in the second stage of labor. In any of these situations, an operative vaginal delivery might be indicated to minimize the effects of labor on the mother's underlying medical condition.
Before any forceps delivery can be attempted, the cervix must be completely dilated and the membranes (bag of waters) must be ruptured. The baby's head must be at or below zero station (engaged), meaning that the largest diameter of the baby's head has passed through the inlet of the mother's pelvis.
The degree of molding of the baby's head must also be considered. Because the fetal skull is not a single fused structure, the baby's head routinely shifts to a position of least resistance as it proceeds through the birth canal. This is called molding. The extent of molding will determine the type (shape) of forceps used.
Before a forceps-assisted delivery is performed, it is also critically important that the position of the baby's head be precisely known:
- Is the baby in an occiput anterior position (this is the most common position with the baby facing back toward the mother's tailbone), occiput transverse position (facing toward one side or the other), or occiput posterior position (facing toward the mother's pubic bone)?
- Is the baby's head symmetric within the pelvis? Or is the provider able to feel more of one side (left or right) of the baby's head than the other? Asymmetric presentation is called asynclitism and can cause a larger diameter of the baby's head to present with a much greater risk of inadequate labor progress.
- Is the baby's head presenting with the occiput (the top and back of the head, the area sometimes seen as a bald spot)? If the baby's forehead (called a brow presentation) or the face are presenting, then very different maneuvers must be considered.
Needless to say, it is extremely important to know the exact position of the baby's head because improper placement of the forceps could cause injury to mother and/or baby. Abnormal position of the baby's head may suggest other problems such as disproportion of the size of the baby and the size of the mother's pelvis or congenital abnormalities. Babies with abnormalities more often present in positions other than an occiput first.
Prerequisites for Forceps Delivery:
- cervix is completely dilated;
- membranes are ruptured;
- baby's head is engaged (at zero station or lower);
- exact station and position of baby are known;
- extent of molding of baby's head evaluated;
- size and shape of mother's pelvis assessed and weight of baby estimated;
- adequate anesthesia administered; and
- attendance of experienced and well-trained provider.
Another prerequisite for forceps-assisted vaginal delivery is assessment of the dimensions of the mother's bony pelvis and estimation of the baby's weight. There is no precise formula (size and shape of pelvis in relation to the size and weight of the baby) for predicting which babies can and will be delivered safely. However, an experienced provider should be able to determine whether or not a woman's bony pelvis is of normal size and configuration. He or she should also be able to provide a generally reliable estimate of the baby's weight (plus or minus 15%).
All of these variables, particularly complete cervical dilation, station and position of the baby's head, and assessment of the mother's birth canal, are documented in the medical record.
An additional prerequisite for operative vaginal deliveries is the availability of adequate anesthesia and facilities. The placement of forceps hurts above and beyond the pain of normal labor. A pudendal block (which blocks the nerves that relay pain sensations from the mother's perineum) is the minimum anesthesia for a forceps delivery. Regional anesthesia (spinal or epidural) should be considered for procedures involving more extended pulling or rotation. In some situations, general anesthesia may be necessary. Forceps deliveries should generally be performed only in facilities capable of promptly performing a cesarean section delivery if the attempted forceps delivery is unsuccessful for any reason.
Finally, only an experienced and well-trained provider should perform an assisted-vaginal delivery. The provider uses his or her knowledge of the mechanisms of normal labor, the details of the labor of the specific patient, and findings from physical examination, as outlined above, to perform a safe and successful forceps delivery. The skilled provider also knows when to abandon the procedure in favor of cesarean birth.