Stainless steel devices are mentioned primarily for their historical significance and because they have served as prototypes for plastic devices in use today. Early in 2000, the labor and delivery unit utilized by the authors attempted to buy new Malmstrom and Bird cups in order to teach our OBGYN residents the proper use of these devices. However, the European manufacturers declined to sell these devices to buyers in the United States. Their stated reservation was due to U.S. product liability laws and their wish to avoid any potential medicolegal entanglements.

The Malmstrom vacuum extractor (Fig. 26.2) is a shallow, mushroom-shaped stainless steel cup, with two
vacuum hoses, a traction chain and attached metallic disk, a traction handle, and a vacuum source. The center of the cup has a metallic suction port through which the traction chain passes. The traction chain is attached to the cup by a metallic disk that is inserted within the cup to prevent the fetal scalp from being pulled into the vacuum port. The margin of the metallic disk is scalloped at regular intervals such that the vacuum may be developed beyond the underside of the disk and onto the fetal scalp. The Malmstrom vacuum extractor can be assembled in seconds. After its use the device is easily disassembled, and the components are washed, autoclaved, and packaged for future use.

The Malmstrom cup has an inverted lip such that the diameter of the opening is smaller than the internal diameter of the cup. When the cup is placed on the fetal scalp and vacuum is established, a small artificial caput forms, termed the chignon. When the fetal scalp fills the internal dimensions of the cup, the scalp underlies the opening of the cup in a “key-in-lock” fashion. This allows a considerable traction force to be applied before cup detachment occurs.

The utility of the Malmstrom cup is limited by a combined vacuum port and traction apparatus in the dome of the cup, which makes appropriate application somewhat difficult in positions of the fetal head other than occiput anterior (OA). In 1969, Bird developed two modifications (anterior and posterior) of the Malmstrom cup to increase the versatility of the vacuum extractor for proper placement with difficult positioning of the fetal head. Bird separated the vacuum port and the traction apparatus (Fig. 26.2). The traction chain remained anchored to the center of the cup, while the vacuum port was attached eccentrically to the dome of the anterior cup. The vacuum port was attached laterally for the posterior cup. With these modifications, the vacuum tubing exited in the same plane as the cup, a change which enabled the physician to better maneuver the cup into its proper location within the maternal pelvis. In even later versions of the Bird cups, the central traction chain was replaced by a nylon cord anchored to the edges of the cup and to a traction bar for physician convenience.

There are several types of plastic or silicone vacuum cups currently in use in the United States (Fig. 26.3). The cups are separated into three groups, depending on the shape of the vacuum cup: funnel, bell, or mushroom. Of these, the funnel-shaped cups are the least used. The prototype for this vacuum extractor was based on the original Kobayashi silastic cup, introduced in 1973. The diameter of this device (65 mm) is the largest of any of the commercially available cups, and therefore its size obviates the need for a chignon to form in order to achieve appropriate traction. This device also has a vacuum release valve on the stem, which allows the operator to reduce vacuum pressure between contractions, if desired. Variations on the original Kobayashi design are available from several vendors. A much lower rate of neonatal scalp trauma was reported with the Kobayashi cup in contrast to experiences with stainless steel cups, a finding that was corroborated by five randomized studies of the silastic cup versus the stainless steel cups. Although the Kobayashi vacuum extractor was noted to effect delivery in less time than stainless steel devices, a higher failure rate occurred, especially when the fetal head was in the OP presentation.

Bell-shaped vacuum cups are widely available from several vendors in the United States. One example is the Mityvac device (Cooper Surgical, Trumbull, CT), which was compared with a silastic funnel-shaped cup and Tucker-McLane forceps in a prospective, randomized study of 118 delivered patients by Dell in 1985. Trauma to the maternal genital tract trauma was noted in 48.9% of the women delivered by forceps as compared with 36.1% and 21.6% of the women delivered by the silastic and bell-shaped cups, respectively. This represented a statistically significant reduction in maternal genital tract trauma with use of the bell-shaped vacuum device. Success rates using the bell-shaped cup (89.2%) versus forceps (93.3%) were not significantly different. However, there was a significantly higher rate of cephalohematoma formation in the neonates delivered with vacuum devices (funnel-shaped cup, 13.9%; bell-shaped cup, 16.2%) than with forceps (2%). Caput and
scalp discoloration was more apparent with the bell-shaped cup than with the funnel-shaped cup. With regard to the utility of the soft-cup vacuum devices, Dell’s group concluded that “the dramatic usefulness of these instruments to quickly deliver multiparas whose infants experienced fetal distress in late labor was far more impressive than their performance as outlet instruments in nulliparas.”

The first generation of mushroom-shaped cups represented an apparent attempt to produce a plastic version of the Malmstrom stainless steel cup. Several vendors offer disposable mushroom-shaped vacuum cup devices made of semirigid plastic; one of the more popular devices has been the M-cup (Mityvac). The efficacy of this cup was tested prospectively against the obstetric forceps in a large randomized clinical trial by Bofill in 1996. Both devices were comparably effective as tools to accomplish vaginal delivery, but deliveries with the M-cup were accomplished in less time and with less maternal genital tract trauma. As with nearly all other studies of vacuum and forceps, the clinical diagnosis of neonatal cephalohematoma was made significantly more often after vacuum delivery.

The first generation of mushroom-shaped vacuum cups faced the same problems as the original Malmstrom stainless steel device—limited maneuverability. They were, however, more easily maneuvered than funnel- or bell-shaped cups within the maternal introitus because the traction stem could be bent at a 90-degree angle with respect to the cup. Nevertheless, the combined and centrally located vacuum port and traction stem limited the ability of the physician to place the vacuum cup on the median flexing point, especially in cases of difficult positioning of the fetal head such as OP or OT positions or in the presence of significant asynclitism. Past experience with improvements to the stainless steel cups afforded a design solution to this shortcoming as a plastic equivalent of the Bird posterior cup. In 2001, Vacca tested the OmniCup (Clinical Innovations Inc., Murray, UT) and found that it was quite useful for both nonrotational and rotational vacuum-assisted vaginal deliveries (Fig. 26.3). Vacca was able to achieve a median flexing application in 90% of applications, which resulted in “autorotation” in 32 of 33 cases in which rotation was expected.

The disposable plastic or silicone vacuum cups currently in use in the United States are marketed with a pistol grip hand pump that is connected to the cup by vacuum tubing (Fig. 26.3). A filter in the vacuum tubing prevents the suctioning of liquids or other debris into the pump. While it is possible to sterilize this pump, it is most commonly managed by a nurse or other attendant while the physician attends to the delivery. More recent versions of the mushroom vacuum cup are marketed with a disposable vacuum pump attached to the cup by a slender vacuum tube with an internal chain. This pump also contains a traction bar with a vacuum gauge and a vacuum release button. This allows the physician to better control the appropriate timing of vacuum pressure and traction.

The recommended operating vacuum pressures for the majority of cups, whether stainless steel or plastic, is from 0.6 kg/cm² to 0.8 kg/cm² (about 500 to 600 mm Hg). The original stainless steel devices used a device that resembled a bicycle hand pump to achieve the required vacuum strength. The vacuum tubing was attached to a stoppered vacuum bottle that had ports for the vacuum pump and a vacuum gauge (Fig. 26.2). Alternatively, a portable electric vacuum pump or the hospital’s wall suction system could be used to generate vacuum pressure. These systems are used rarely, if at all, in the United States for vacuum-assisted delivery.

Newer vacuum devices permit the rapid achievement of required vacuum pressure as a single step over several seconds, much faster than the slow and stepwise increase in pressure required with the original Malmstrom device. There is no difference between the final recommended vacuum pressure to achieve for plastic or silicone cups compared with the original stainless steel cups. With steel, the vacuum pressure is slowly brought to 600 mm Hg and is maintained at that level until delivery is accomplished—there is no reduction between uterine contractions and traction efforts. However, with the plastic cups, some authorities have recommended that the level of vacuum pressure should be reduced from 600 mm Hg during traction and contractions to 100 mm Hg during rest. The rationale for this recommended reduction in vacuum pressure is to expose the fetal scalp to the least amount of time at high vacuum pressures. A randomized trial of the intermittent versus continuous techniques of vacuum pressures during delivery with a mushroom-shaped cup failed to demonstrate any difference in neonatal outcomes. Regardless of the technique, however, the longer a vacuum cup resides on the fetal scalp, the greater is the likelihood of cephalohematoma formation and other cosmetic scalp lesions.

The following list summarizes the recommended steps for use of a mushroom-shaped cup to accomplish vacuum-assisted vaginal delivery, analogous to the check-offs that a pilot undertakes while readying a plane for flight:

The indications for vacuum-assisted delivery are nearly identical to those for obstetric forceps. The most common indications include a prolonged second stage of labor or nonreassuring fetal status. Other indications include maternal exhaustion and maternal illnesses in which maternal expulsive efforts should be limited. The indication for vacuum delivery should be included in the delivery note portion of the medical record.

It is important for the physician to perform a careful assessment of the fetal head with regard to the size and position of the caput succedaneum and the amount of molding. Severe molding of the fetal head may indicate cephalopelvic disproportion. The method of Stewart is used to describe the amount of molding by examination of the parietal bones (Fig. 26.5). Safe and successful vacuum-assisted delivery is contingent on an appropriate application of the cup onto the fetal head. It is very important that the cup be placed on the median flexing point, as defined by Vacca (Fig. 26.4). To achieve the correct median flexing application, the center of a 60-mm cup should be placed 3 cm from the posterior fontanelle and symmetrically astride the sagittal suture. In this application, one edge of the cup will encroach on the posterior fontanelle, while the opposite edge will be about 3 cm from the anterior fontanelle. The median flexing point is located at the emergence of the mentovertical diameter and is about 3 cm anterior to the posterior fontanelle and in the midline (Fig. 26.6). The fetal head is considered to be optimally flexed when the mentovertical diameter points in the direction of the pelvic axis. The center of the vacuum cup should be placed over the median flexing point so that it is symmetrically astride the sagittal suture. Correct application of the vacuum cup as described is important because traction in the direction of the pelvic axis will maintain flexion of the fetal head and minimize or eliminate any asynclitism. Thus, the maternal pelvis is presented with the most favorable diameter of the fetal head, and atraumatic delivery is optimized.

There are several potential consequences of suboptimal cup placement. Asymmetric placement of the vacuum cup astride the sagittal suture (a paramedian application) will
produce asynclitism when traction is applied. If the center of the cup is placed too far anteriorly, subsequent traction will produce deflexion of the fetal head (deflexing application). If the placement of the cup is both paramedian and deflexing, successful and safe delivery is unlikely.

The least resistance to delivery of the fetal head occurs when the direction of vacuum traction is parallel with the pelvic axis. Traction should be perpendicular to the vacuum cup. Angular (off-center) traction commonly produces lift at the far edge of the cup, which can lead to disconnects or “pop-offs.” If traction at an angle cannot be avoided secondary to asynclitism or deflection of the fetal head, the physician may be able to compensate for this off-center traction by using the thumb or index finger of the nontraction hand to apply counterpressure on the far side of the cup. This is the so-called three-finger grip, which also assures that descent of the fetal skull occurs with vacuum traction and maternal expulsive efforts.

Physicians should never apply torsion to the vacuum cup when it is used to deliver an infant from an OP or OT presentation, as this can result in fetal scalp injury. Straight axis traction of a properly placed cup will often produce rotation to the OA position when the fetal head encounters resistance from the maternal levator musculature in a pelvis of adequate size for vaginal delivery. This is termed autorotation, a phenomenon that is commonly seen as the fetal head descends in both spontaneous as well as vacuum-assisted delivery. Vacuum traction should be applied only in concert with maternal expulsive efforts.

The physician should be willing to abandon an attempt at vacuum-assisted delivery if it does not go well and complications are noted. If fetal scalp trauma is observed with the vacuum cup, the cup should be removed and delivery accomplished otherwise. As the length of time a vacuum cup is on the fetal head increases, so does the potential for development of a cosmetic scalp lesion and cephalohematoma. Manufacturers of vacuum delivery devices frequently recommend that the fetal scalp be subjected to no more than 10 minutes at high vacuum pressures. Because recording of the cumulative time that the fetal scalp has been at high vacuum pressures is a cumbersome and frequently inaccurate procedure, we recommend that the length of time that a cup spends on the fetal scalp be limited to 20 minutes. It is the authors’ opinion that if a vacuum cup pops off three times, it is wise to terminate any further attempt at vacuum delivery. Pop-offs may indicate the presence of a nonmedian or deflexing cup application, angular traction, or cephalopelvic disproportion. Perhaps the most important tenet of vacuum delivery is that if a proper application and adequate traction does not produce descent of the fetal head, the procedure should be terminated without waiting for three pop-offs or for 20 minutes to elapse. These deliveries are an excellent exercise in physician judgment and discretion.

After each vacuum delivery, it is recommended that the fetal scalp be examined to assess the position of cup placement and to document scalp trauma. Nursery physicians should be informed that the infant was delivered by vacuum so that attention can be focused on the fetal scalp after delivery. Documentation of the vacuum delivery is of obvious importance, with a detailed written, dictated, or recorded-by-computer entry in the medical record. Details of importance to record include the indication(s) for the procedure, the instrument used, the station and position of the fetal head at the time the cup was applied, identification of the vacuum procedure as midpelvic or low or outlet in type, the number of pop-offs, and the length of time the cup was on the fetal head. Caput, molding, asynclitism, and autorotation, if encountered or noted during delivery, are documented as well. The type of analgesia provided and any maternal or fetal trauma also should be documented.

Any physician who performs a substantial number of vacuum-assisted deliveries will occasionally need to abandon a vacuum procedure for one or more of reasons noted previously. In this situation, the physician has three options to consider. First, spontaneous delivery may be possible if there are good maternal expulsive efforts and the fetal head is on the pelvic floor. Second, cesarean delivery is clearly indicated if the fetal head is in the midpelvis or at low pelvic station with suspicion of cephalopelvic disproportion. Third, obstetric forceps can be used to accomplish vaginal delivery after a failed vacuum attempt, especially if the fetal head is deep within the pelvis. These “sequential operative vaginal deliveries” (vacuum first and then forceps or forceps first and then vacuum) are controversial. Some physicians consider initial use of a midpelvic vacuum extractor to be appropriate in order to convert what would have been a difficult midforceps procedure into a much easier low- or outlet-forceps procedure.

Small studies by two groups of investigators were unable to demonstrate any additional neonatal complications associated with “sequential” operative vaginal deliveries. The frequency of this sequential operative vaginal delivery ranged from 4% to 27% in nine studies of vacuum and forceps deliveries. However, a population-based study of fetal intracranial hemorrhage demonstrated that the risk of fetal intracranial hemorrhage clearly was increased after the sequential use of instruments as compared with spontaneous delivery, cesarean delivery, or the single use of either forceps or vacuum.

Another large study of the sequential use of instruments was produced by Gardella. In this study, the sequential use of instruments was associated with significantly higher rates of neonatal intracranial hemorrhage, brachial plexus injury, facial nerve injury, neonatal seizures, and depressed 5-minute Apgar scores. Thus, the sequential use of instruments for operative vaginal delivery is not recommended except in dire circumstances.

A cephalohematoma is a self-limited injury that is caused by the rupture and bleeding of an emissary vein into the potential space just beneath the periosteum of the neonatal parietal bone (Fig. 26.7). The periosteum of the
parietal bone is firmly attached at the periphery, and only a limited amount of fetal blood can collect in this potential space. Cephalohematomas are diagnosed more commonly after vacuum extraction as opposed to forceps delivery. They typically resolve spontaneously over the course of a few days without long-term sequelae, although neonatal hyperbilirubinemia can develop. Most often, a cephalohematoma will not cross the suture lines of the skull, but edematous scalp can render the examination difficult and make the diagnosis challenging. Illustrative of this is the ultrasound confirmation of only three cephalohematomas in 12 neonates thought to have the condition. The other 9 infants had edematous scalps and not cephalohematomas.

Factors associated with cephalohematoma formation were studied in a Mississippi series of 322 vacuum extraction procedures performed with the semirigid mushroom-shaped cup. The rate of cephalohematoma formation in this study was 11%. Significant contributors to the diagnosis of neonatal cephalohematoma included the duration of the vacuum procedure and the amount of asynclitism at the time of cup placement. Asynclitism easily leads to a paramedian cup application that is productive of the chignon over one parietal bone more so than the other, which enhances the possibility of a false diagnosis of cephalohematoma.

A much more serious and potentially fatal complication of vacuum extraction is a subgaleal (subaponeurotic) hemorrhage, in which a scalp vessel ruptures distal to the level of the periosteum where blood can accumulate in the layer of loose connective tissue known as the subgaleal or subaponeurotic space (Fig. 26.7). This potential space is very large and extends from the orbital ridges anteriorly, to the nape of the neck posteriorly, and to the zygomatic arches laterally. This space can easily accommodate the entire blood volume of a term newborn, even if filled only to a 1 cm depth. The most common physical finding with a subgaleal hemorrhage is a fluctuant mass that extends over the cranial sutures and fontanelles. This usually is accompanied by edema and bruising that extends posteriorly into the neck and laterally around the ears. The fluctuant mass can reach the upper eyelids and the root of the nose. The infant will commonly have evidence of hypovolemic shock. Shock may manifest hours after delivery or even later in the nursery. Subgaleal hemorrhage also has been associated with midforceps delivery, leading at least one investigator to conclude that instrumental delivery is the principal predisposing factor for this lesion. The incidence of subgaleal hemorrhage is estimated to occur in 4 of 10,000 spontaneous vaginal deliveries and in 59 of 10,000 vacuum-assisted deliveries.

The 1998 FDA public health advisory primarily was directed at alerting all physicians who practice vacuum-assisted vaginal delivery to be very aware of subgaleal hemorrhage as a potential complication. Advising nursery personnel that a vacuum-assisted vaginal delivery has been performed also is key to facilitating the early diagnosis of a subgaleal hemorrhage.

Although intracranial hemorrhage in the term infant often is associated with traumatic operative vaginal delivery, it can occur after spontaneous delivery as well and have profound neonatal consequences (Fig. 26.7). In 1990, Hannigan and coworkers reported three cases of tentorial hemorrhage that were associated with soft-cup vacuum extraction deliveries. They reasoned that vacuum delivery could produce vertical stress in the occipitofrontal diameter, thereby causing tentorial venous hemorrhage. Nine other cases of tentorial subdural hemorrhage in term newborns were reported by another group, with five cases following delivery using the vacuum extractor. Seven of the nine infants were neurologically normal at 13 months of age. One infant delivered by vacuum extraction required a ventriculoperitoneal shunt for progressive hydrocephalus.

Vacuum extraction typically is avoided in the fetus that is very preterm because of the increased risk for intracranial hemorrhage at earlier gestational ages. There is no evidence-based gestational age threshold on which to base practice, but most clinicians avoid vacuum extraction altogether at <34 weeks gestation. Two small retrospective studies have been published that were unable to demonstrate an increased risk of intracranial hemorrhage in preterm infants delivered via the vacuum. Finally, Towner and colleagues utilized a population-based study to show that the rates of intracranial hemorrhage are not statistically significantly different for vacuum-assisted delivery, forceps delivery, and for cesarean delivery performed during labor. However, those deliveries accomplished by the sequential use of instruments (vacuum, then forceps) were associated with a significantly higher rates of intracranial hemorrhage.

Neonatal retinal hemorrhage after vaginal delivery is quite common. In 1974, Ehlers and colleagues noted neonatal retinal hemorrhage in 28% of newborns following spontaneous delivery, 38% with forceps delivery, and 64% after delivery with the Malmstrom vacuum extractor. Others reported the incidence of moderate to severe retinal hemorrhages in infants delivered with the soft plastic bell-shaped cup to be 18% with spontaneous deliveries, 13% with forceps, 28% with vacuum, and 50% in infants delivered using sequential forms of operative vaginal delivery. Multiple logistic regression analysis has been used as well to identify the factors associated with moderate to severe retinal hemorrhage. These have included vacuum delivery of low–birth-weight infants, short second stages of labor, fetal acidemia, and the sequential use of vacuum-then-forceps
for delivery. Neonates delivered by vacuum extraction typically will have higher rates of retinal hemorrhage. Neonatal retinal hemorrhages have not been demonstrated to have long-lasting effects. Following a 5-year period of study, children delivered by random assignment either to vacuum or forceps extraction demonstrated no difference in visual problems.

Hundreds of obstetric forceps have been developed for utilization in this country and elsewhere in the world—there are many choices (Fig. 26.8). Most obstetricians, however, comfortably and competently use no more than three or four different types of instruments in their practices.

Obstetric forceps are a paired instrument, fashioned of two branches that articulate with one another by a lock. The branches (left and right) are side specific and named according to the side of the maternal pelvis into which it will be applied. Before using any obstetric forceps, the obstetrician should be certain that the two branches of the pair constitute a matched set that is symmetrical when articulated. Application techniques are described below.