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Clinical Reviews


Operative vaginal delivery: 10 components of success

The need for forceps or vacuum should not be determined on the fly, but anticipated and evaluated, with a willing patient

February 2007 · Vol. 19, No. 02

IN THIS ARTICLE

Operative vaginal delivery is a dying art. National databases in the United States and elsewhere have shown this trend for decades.1 Women no longer can be reliably predicted to prefer operative vaginal delivery over cesarean section, and providers caring for delivering mothers (and their families) should not assume that they do. Nor does the 20th century paradigm of operative vaginal delivery as the accepted “next step” between spontaneous vaginal delivery and cesarean section hold up, given the decreased maternal and neonatal morbidity and mortality associated with modern techniques of cesarean section. Nevertheless, operative vaginal delivery remains a viable option in some cases.

This article—based on personal opinion and experience, as well as published data whenever possible—describes 10 selected aspects of operative vaginal delivery, offering recommendations for each.

1. Consider obstetric history

How a woman fared in previous deliveries has a bearing on the current delivery. For example, if she has a history of persistent occiput posterior position, as in the case described on page 56, she may have an anthropoid pelvis, placing her at increased risk for another malposition.1 In such cases, the patient should be counseled about the potential for operative vaginal delivery, and the risks and benefits should be discussed prenatally.

A history of obesity, excessive weight gain, and glucose intolerance should be considered warning signs of a large-for-gestational-age infant.

2. Ensure adequate informed consent

Patients should be informed of the risks of any procedure they are offered, and operative vaginal delivery—like any operative procedure—has definite risks.

It is unbalanced to mention only the perceived benefits of a procedure and to avoid the discomfort of discussing the potential significant fetal and maternal injury that may result from a procedure. It is far better for the patient and her family to learn—before an adverse outcome occurs—that forceps delivery sometimes leads to maternal and fetal lacerations, and that operative vaginal delivery can be associated with an increased risk for shoulder dystocia in some circumstances.

The best way to educate patients about operative vaginal delivery is during prenatal care. I recommend a written informed consent document similar to the one used for cesarean section. If such a form is not signed during the course of office prenatal care, it should be offered upon admission for delivery.

In some cases, operative vaginal delivery may be safer than cesarean

Operative vaginal delivery clearly increases the risk of neonatal intracranial bleeds when compared with normal spontaneous vaginal delivery or elective cesarean section.2 However, a patient should understand that cesarean section carries a risk of neonatal intracranial hemorrhage similar to that of operative vaginal delivery once a woman has labored to complete dilation and pushed for some time.2 In fact, a baby with a well-engaged head can experience significant increases in intracranial pressure during cesarean delivery when concerted efforts have to be used to deliver a deeply engaged fetal head out of a hysterotomy incision. Such maneuvering can also injure the fetal neck and brachial plexus.

3. The abdominal examination is critical

Examination of the maternal abdomen helps to confirm the fetal lie and presentation and may give an idea of the position of the fetal back in relation to the uterine midline. If the fetal back cannot be felt or is palpated far laterally, the fetus may be in an occiput posterior or transverse position. Often this knowledge helps the examiner make sense of an otherwise difficult vaginal examination.

Estimate fetal weight

Fetal weight estimations from a careful abdominal examination can be as accurate as ultrasonographic evaluation.3 It is strongly recommended that fetal weight be estimated and considered in context with maternal diabetes, obesity, excessive weight gain, and previous ultrasound examinations before operative vaginal delivery is undertaken.

Is the fetal head engaged?

The average term (3,200 g) fetus has a basovertical head diameter of approximately 9 to 10 cm,4,5 and the average adult finger has a diameter of 2 cm (one fifth of the head). Using this information, an estimate of how many “fifths” of the fetal head are above the pelvic brim can be made by evaluating how many fingerbreadths of fetal head can be palpated above the symphysis pubis on abdominal examination.

Crichton4 described this method in 1974, and it is an extremely useful and underutilized technique, in my opinion. He stated that no more than two fifths (2 fingerbreadths) of an unmolded fetal head should be palpated abdominally once the occiput is felt at the ischial spines. If three fifths or more of the fetal head is still palpable above the pubic symphysis, regardless of whether there is bone palpated at or below 0 station on vaginal examination, consider the head unengaged and avoid operative delivery.

It is quite possible to feel the fetal skull bone below the ischial spines and still have an unengaged head.5 This is due to molding of the head and elongation of the basovertical diameter. When this occurs, the widest diameter of the fetal skull remains above the plain of the pelvic brim (unengaged), even though the lowermost point is felt below the spines on vaginal examination. A graphic example of such an elongated basovertical diameter can be seen in the so-called cone-head baby.

At examination, fetal head should be in occiput anterior position

In order to best use the abdominal examination to assess the amount of fetal head above the pelvic brim, the fetal head must be in an occiput anterior position. This is because the occiput is sometimes difficult to palpate in a posterior or transverse position, and the obstetrician may incorrectly assume full engagement. This further underscores the importance of a careful maternal abdominal examination and the location of the fetal spine.

Abdominal examination is more informative than vaginal examination

Knight and colleagues6 studied the relative value of abdominal and vaginal examinations in the determination of fetal head engagement. They examined the records of 104 women who had been evaluated by both methods prior to attempted operative vaginal delivery. Successful vaginal delivery was correctly predicted using abdominal criteria (94%) more often than using vaginal criteria (80%) (P<.01).

Was delivery successful—or a barely averted disaster?

E.D., a 32-year-old gravida 4 para 3, presents at 39 weeks’ gestation with spontaneous rupture of membranes in early labor. Her 3 deliveries thus far have all been vaginal, with the infants ranging in weight from 3,700 to 3,900 g. Two of these infants were delivered with vacuum extraction because of occiput posterior position and a prolonged second stage.

E.D.’s prenatal course has been relatively uncomplicated except for a 43-lb weight gain (she weighs 240 lb) and a borderline 1-hour glucose challenge test. She also had 1 abnormal value on a 3-hour glucose tolerance test. Her prenatal pelvic examination was documented as “adequate.”

In early stages, all appears normal

On admission, E.D. is dilated 4 cm with 70% effacement and a cephalic presentation at -2 station. Electronic fetal monitoring is reassuring, and she is contracting regularly every 6 minutes, with moderate pain. The physician on call instructs the nurse to start oxytocin if there is no progress in 2 hours, and to call anesthesia to give an epidural if the patient requests it. E.D. asks for, and is given, an epidural 2 hours later, when her cervix is dilated 5 cm.

The next morning, a different physician examines her and reports a rim of cervix remaining, with the fetal head at 0 to +1 station. He asks E.D. to push, and the rim is reduced over the infant’s head. The patient is instructed to continue pushing with contractions. The physician writes the admission (and only predelivery) note: “32 yr old G4P3, term, SROM, good FHTs, good progress, complete, 1+ station, clear fluid. Anticipate vaginal delivery.”

When progress stalls, mother tires

E.D. pushes well with adequate contractions for 2.5 hours, with minimal descent of the head and increasing caput and molding. The physician examines her again and reports that the baby is at +2 station. He also suggests the use of the vacuum extractor, because the patient is becoming exhausted and the baby is “quite big.” The obstetrician appears somewhat hesitant when applying the vacuum and remarks to the nurse that he “thinks the baby is in a left occiput anterior position” but is not “100% sure.”

When vacuum fails, a switch to forceps

After 2 attempts with the vacuum extractor, during which there are 2 “pop-offs,” the physician asks for Simpson forceps, adding that he thinks the baby is now in right occiput posterior position and he needs to “get a better grip on the baby’s head.” The forceps are applied with some difficulty, necessitating 2 reapplications.

After 5 contractions (and 6 pulling efforts), a baby boy is delivered. Because of a delay in delivery of the shoulders after delivery of the head, the physician places the patient in McRoberts position and has a nurse apply suprapubic pressure, and no further difficulties are encountered.

Large baby has brachial plexus injury

The infant weighs 4,200 g and has Apgar scores of 3 and 8, as well as a small laceration on his forehead, moderate flaccidity of the left arm, and an elongated head. The mother has a 4th-degree laceration that is repaired with some difficulty.

The delivery note reads: “Assisted vaginal delivery, 4,200 g male, 3 vessel cord, 600 cc estimated blood loss, 4th-degree laceration repaired in layers.” E.D. ultimately requires 2 U of blood on postpartum day 2 for symptomatic anemia.

Mother and baby are discharged on postpartum day 4 in stable condition. The infant has a brachial plexus injury that resolves within 6 weeks.

Lessons learned

Among the mistakes the obstetrician made in this case are a failure to take the obstetric history into account, omission of a comprehensive abdominal exam, ignoring signs of a large baby, and lack of a plan for emergent cesarean section.

4. Keep molding in mind

Some (up to +2) occipito-parietal molding may be normal in the late stages of delivery (ie, the occipital bone slips under the 2 parietal bones, but can be easily reduced), but severe parieto-parieto molding is never normal and should be interpreted as a sign of relative or absolute cephalopelvic disproportion. FIGURE 1 shows a classification system for molding.

FIGURE 1 How to characterize the degree of molding

Excessive molding may lead to tears in dura and underlying vessels.

Traction plus severe molding may increase the risk of intracranial injury

The most frequent causes of molding are asynclitism and deflexion of the head, commonly seen in occiput posterior and transverse positions. Correction of the asynclitism and malposition may correct the molding and allow safe vaginal delivery. Traction on a head with severe molding may increase the risk of intracranial injury.

Using maximum likelihood logistic regression analyses, Knight and colleagues6 demonstrated that the factor of greatest importance in determining whether a case would be allocated to engaged versus unengaged groups was molding (odds ratio 2.17; 95% confidence intervals 0.75–6.27). The authors concluded that when abdominal and vaginal assessments produce different findings, the major factor responsible is molding. They noted that data derived from vaginal examination alone may be misleading when molding is present.

Continued...
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