Dr. Belfort outlined a strategy for determining the likelihood of success of operative vaginal delivery: “the rule of fifths.” I agree that this rule can be very helpful at the time of abdominal palpation, but it can be difficult to apply when the patient is obese. This is discouraging because the incidence of obesity is especially high in the United States, and obese women have an increased incidence of macrosomia and difficult operative delivery.
Another way to determine the likelihood of success is to ask the patient to bear down as you perform a vaginal examination. If the fetal head exhibits mobility and some descent, success is more likely. A “tight fit” would be an indication for a trial of forceps in the operating room.
In some cases, an ultrasound scan may help determine the position of the fetal head.
The most important determination is whether forceps delivery can be performed in the labor and delivery suite or is better limited to a trial of forceps in the operating room. The proper application of the forceps is vital to avoid maternal and fetal injury.
Raymond Michael, MD
Dr. Belfort responds: Informative abdominal exam is possible even in the obese
I agree that determining the number of fifths of the fetal head above the maternal symphysis pubis may be more difficult in an obese patient. However, even in an extremely obese woman, it is still possible to elevate the pannus and feel the symphysis in most cases (even if an assistant has to help). If there is any doubt that the head is palpated, further efforts may be appropriate to ensure that the fetal head is engaged, including, as Dr. Michael suggested, use of ultrasound.
While I agree in theory that descent of the fetal head with maternal pushing efforts is important, I would not rely solely on this mobility to determine whether or not a trial of forceps or vacuum is indicated. Because the basovertical diameter of the fetal head can be elongated, it is possible to palpate the leading edge of the skull below the ischial spines and still have an unengaged fetal head. This is exactly the circumstance in which a vaginal examination will give false reassurance of the chance of success. In this circumstance, although part of the skull is below the plane of the ischial spines, the widest diameter of the fetal head (usually the biparietal diameter) is still above the plane of the maternal pelvic brim, and the fetal head is unengaged.
I would argue against moving ahead with a “trial of forceps in the OR” in cases with a “tight fit.” As discussed in the article, significant molding implies stretching of the underlying soft tissue. In my opinion, proceeding with an operative vaginal delivery in the case of a fetus with 3+ molding would be riskier than is justified. Operative vaginal delivery should be offered only when it is almost certain to succeed. For that reason, I would also caution against using a trial of forceps in cases where the outcome is uncertain. Cesarean section may be the safest option in such cases.
I agree completely that liberal use of ultrasound to determine head position and station (if possible) should be encouraged.
I recommend that any forceps delivery that is anything other than an outlet delivery take place in the operating room. In addition, I recommend always having neonatal and anesthesia backup readily available with any operative vaginal delivery attempt unless it is an emergency.
Finally, I agree that the correct application of the forceps is essential. In fact, the most important part of the forceps procedure is what happens before the actual application of traction! If the correct indications have been followed, the patient has been properly assessed and prepared for the procedure, and if all ancillary services are available, the traction effort is usually the least stressful part of the delivery, since it is bound to succeed.