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.