INTRODUCTION — Vacuum extraction accounts for over 80 percent of operative vaginal deliveries in the United States [1]. The technique for vacuum-assisted vaginal delivery will be reviewed here. An overview of methods for operative vaginal delivery, including choice of vacuum versus forceps, and risks and outcomes, can be found separately. (See "Operative vaginal delivery".)

INDICATIONS AND CONTRAINDICATIONS

Indications — An operative vaginal delivery (vacuum or forceps) should only be attempted when a specific obstetric indication is present [2,3]. The three major categories of indication are prolonged second stage of labor, nonreassuring fetal status, and shortening the second stage for maternal benefit, but there is no absolute indication. The indications and prerequisites for operative vaginal delivery are discussed in more detail separately. (See "Operative vaginal delivery", section on 'Indications' and "Operative vaginal delivery", section on 'Prerequisites'.)

Contraindications

●Vacuum extraction

•Historically, experts have recommended avoiding use of vacuum devices to assist delivery before 34 weeks of gestation due to a perceived increased risk of birth injuries in preterm infants. In a registry review of 40,764 preterm births in Sweden, 3.3 percent of preterm births <34 weeks of gestation were delivered by vacuum extraction despite this recommendation [4]. Intracranial hemorrhage occurred more frequently with vacuum extraction than intrapartum cesarean delivery at this gestational age (72/1000 versus 59/1000). While these data were gathered retrospectively and confounded by indication, avoiding vacuum extraction in pregnancies less than 34 weeks is a prudent approach.

Prior scalp sampling or multiple attempts at fetal scalp electrode placement are relative contraindications to vacuum extraction because scalp trauma from these procedures theoretically may increase the risk of cephalohematoma or external bleeding from the scalp wound.

●Any operative vaginal delivery

•Suspected fetal-pelvic disproportion is a contraindication to any forceps or vacuum assisted vaginal delivery.

•Known fetal demineralization diseases (eg, osteogenesis imperfecta), maternal Ehlers-Danlos syndrome [5,6], and fetal bleeding diatheses (eg, thrombocytopenia or hemophilia [7]) are generally accepted contraindications to any forceps or vacuum-assisted vaginal delivery because of perceived increased risks of fetal or maternal trauma, but both the absolute and relative risks are poorly defined.

INSTRUMENTATION — Instrumentation consists of a vacuum pump, a cup to attach to the fetal scalp, and some type of handle attached to the cup, which is pulled to generate traction (picture 1).

Vacuum — Suction can be generated manually or with an electrical suction device.

The Kiwi complete vacuum delivery system devices (picture 2), the MityOne one-piece (picture 3), and the Mystic II vacuum all come with a pump integrated into the handle of the device, so the operator controls the vacuum without need for an assistant. Some vacuum devices also come with a traction force indicator, allowing the operator to compare tactile impression with an objective measure of force.

Extractor cup — Vacuum cups may be soft (pliable) or rigid and the shape may be bell or "M" shaped (picture 4). Rigid cups were initially made of metal, but these have been almost completely replaced by rigid plastic, polyurethane, or polyethylene cups. Soft cups are made of plastic, silicone, rubber, or polyethylene. Sizes vary somewhat by manufacturer; any standard cup size may be used for any late preterm or term fetus meeting criteria for vacuum-assisted delivery. (See 'Contraindications' above.)

The optimum type of cup to use for each clinical scenario has not been determined as few randomized trials or comparative studies have been performed.

Soft versus rigid — The performance characteristics of soft versus rigid cups have been examined in numerous trials. A meta-analysis of data from nine trials including 1375 pregnant patients reported the following findings:

●Soft cups were more likely to fail to achieve vaginal delivery than rigid cups (failure rate 14.8 versus 9.5 percent, odds ratio [OR] 1.65, 95% CI 1.19-2.29). Most failures were due to cup detachment.

●Soft cups were associated with less scalp injury than rigid cups (13 versus 24 percent, OR 0.45, 95% CI 0.15-0.60) [8].

●The rate of maternal injury was similar for both cups.

●Rigid cups tended to be more suitable for occiput posterior, occiput transverse, and difficult occiput anterior position deliveries, given their ability to stay attached despite strong traction.

●Soft cups appeared to be more appropriate for uncomplicated occiput anterior extractions where less traction is needed and thus the excess risk of scalp injury could be avoided.

Bell versus mushroom shape — Soft cups are usually bell shaped, while rigid cups tend to be mushroom shaped (picture 4). Conclusive studies comparing the performance characteristics of bell-shaped cups versus the Malmström mushroom or "M" style cups have not been performed. In terms of pure traction force, laboratory studies have demonstrated that bell shaped cups generate significantly less traction force than M-style cups [9].

This difference in traction between bell-shaped and “M” style cups may be the result of the interaction between the cup's edges and the scalp chignon that is formed. Bell-shaped cups tend to draw the chignon into the cup, thereby reducing the available vacuum area and leading to a decrease in cup adhesiveness at the edges. This allows leakage of air and eventual detachments. M-style cups, on the other hand, have a mushroom-shaped design which tends to draw the chignon into the cup while the edges interlock with the base of the chignon, thereby creating a mechanical attachment that seems to compensate for the loss of available vacuum space. These theories have been supported by small clinical trials, although none have definitively answered the question of which cup is superior [10,11].

Occiput posterior position — Because the flexion point on occiput posterior presentations is positioned more posteriorly and higher in the vagina than with occiput anterior presentations, certain adjustments must be employed. Specifically, the cup needs to be placed much deeper in the posterior vagina. This accommodation usually necessitates a vacuum device with a discoid, rather than a bell-shaped, cup and a nonfixed traction cord rather than a firm stem. To meet these needs, special cups have been designed for occiput posterior presentation (table 1).

Handle — Most plastic bell shaped cups have a relatively rigid rod connecting the handle and cup. This impedes accurate placement of the instrument on deflexed or posterior heads. Higher success rates in these malpresentations may be achieved with rigid, plastic "M" cups (table 1), one of which (discussed above) consists of a rigid plastic Malmström-type cup attached by a wire to a unique combined handle/vacuum pump (Kiwi OmniCup (picture 2)).

TECHNIQUE — The clinician must know the indications and contraindications to vacuum-assisted delivery and have expertise in proven techniques (see 'Indications and contraindications' above and "Operative vaginal delivery", section on 'Prerequisites'). Checklists can be helpful as cognitive aids for ensuring safer assisted vaginal deliveries. Checklists have been published by the Society for Maternal Fetal Medicine (SMFM) [12], Royal College of Obstetricians and Gynaecologists [13], and the Society of Obstetricians and Gynaecologists of Canada [14], and can be modified to fit local requirements.

As with forceps, good placement of a vacuum cup requires proper assessment of the fetal position and station, with care taken to identify molding, caput, and asynclitism. In addition, the flexion point is a critical landmark for the safe and effective use of a vacuum. Practitioners need to keep in mind that the location of cup placement becomes the leading point of the fetal head. Unlike forceps, which will usually correct asynclitism after application, failure to place the cup over the flexion point impedes delivery, rather than assisting it.

Patient preparation

●The bladder should be empty (via voiding or catheterization).

●The patient is placed in the dorsal lithotomy position and the fetal presentation, position, and station are confirmed and documented. If findings on digital examination are uncertain, ultrasound can be useful to confirm the diagnosis.

●Antibiotic prophylaxis is not necessary; no benefit has been established, although data are sparse [15].

Anesthesia — Adequate anesthesia can be obtained with neuraxial anesthesia and possibly with a local block. In contrast to forceps, vacuum extraction can be performed without anesthesia if necessary, but the patient will likely experience significant discomfort.

Determine the flexion point — To enable most vaginal deliveries (whether spontaneous or assisted), the fetal head must rotate and flex at the neck to allow the passage of the widest diameter of the head through the pelvis. This pathway is optimized when the mentovertical diameter points in the direction of the delivering pathway.

The flexion point is the location on the fetal head where outward traction pulls the head so as to allow flexion at the neck while keeping the mentovertical diameter in the direction of the birth canal. In the normally molded fetal head, the flexion point is in the midline, over the sagittal suture, approximately 6 cm from the anterior fontanelle and 3 cm from the posterior fontanelle (figure 1). The center of the vacuum cup should be directly over the flexion point.

Since most of the commonly used vacuum cups have a diameter between 50 and 70 mm, when the center of the cup is placed over the flexion point, the edges of the cup should be approximately 3 cm from the anterior fontanelle and at the edge of the posterior fontanelle. The anterior fontanelle is the reference point for checking the application because access to the posterior fontanelle is partially blocked once the extractor cup is in place.

Place the cup — The practitioner spreads the labia and introduces the bell shaped cup by compressing and inserting it into the vagina while angling the device posteriorly. If an M-style or rigid cup is used, the device is flexed at the base of the shaft and inserted sideways into the vagina while angling posteriorly.

When contact is made with the fetal head, the center of the cup is placed over the flexion point and symmetrically across the sagittal suture (figure 1). The entire 360° circumference of the cup must then be digitally inspected to insure that no vaginal, cervical, or vulvar tissues are trapped between the cup and the fetal surface, and that the cup does not cover either fontanelle.

After correct placement of the cup is confirmed, vacuum pressure should be raised to 100 to 150 mmHg to maintain the cup's position. The edges of the cup should again be swept with a finger to insure that no maternal tissues are entrapped. The vacuum cup is now properly in place and the higher suction pressures required for traction can be administered.

Rapidly apply suction — Suction pressure (ie, negative pressure) is measured in various units: 0.8 kg/cm² of atmospheric pressure = 600 mmHg = 23.6 inches of Hg = 11.6 lb/in².

Vacuum suction pressures of 500 to 600 mmHg have been recommended during traction, although pressures in excess of 450 mmHg are rarely necessary (green zone) (picture 5) [16,17]. While lower suction pressures increase the risk of cup "pop-offs," pressures beyond 600 mmHg increase the risks of fetal scalp trauma and cerebral, cranial and scalp hemorrhage.

Rapid application of suction is recommended. Although a slow, stepwise increase in suction over 8 to 10 minutes was initially practiced, randomized trials have demonstrated that rapid application of negative pressure over 1 to 2 minutes reduced the duration of the procedure without compromising effectiveness or safety [18].

The clinician also needs to keep in mind that cup sizes vary among different manufacturers' devices and that cup size affects the overall traction force applied since force = (area under the cup)X(negative pressure). Therefore, as the size of the cup increases, the total force applied will rise even with the same amount of applied negative pressure [19]. As an example, with 600 mmHg of negative pressure, a 50 mm cup will generate 15.7 kg of traction force while a 60 mm cup will generate 22.6 kg of traction force. Whether the greater traction forces associated with larger cup sizes are associated with higher vaginal delivery rates or more fetal morbidity is unclear.

Finally, the notion that the vacuum is "designed to pop-off before damage occurs" is erroneous and should not be considered a safety mechanism. The maximum negative pressure should not exceed 600 mmHg.

Exert traction during contractions — The absolute "safe" traction force for vacuum extraction is unknown. In 1962, one group determined a total traction force of 17.6 kg (172.6 Newton [N]) was typically necessary to affect delivery [20]. Other authors subsequently determined the traction force to be lower, approximately 12 kg (117.7 N) in multiparous patients [21-23]. An observational study of 560 vacuum-assisted deliveries using an OmniCup vacuum device with a traction force indicator found that 86 percent of extractions occurred with ≤11.5 kg (112.8 N) traction and 14 percent with >11.5 kg (112.8 N) traction [24]. One study demonstrated a threefold increase in neonatal intensive care unit admissions when higher traction forces were employed during the first three pulls (>221 N minutes, which is the sum force N during each pull multiplied by its duration in minutes), although these data were too limited to allow generalized clinical recommendations [25]. However, since traction force (measured in kg or N) needs to be individually calculated unless there is a traction gauge and will vary with cup size, negative pressure, and altitude, it is clinically reasonable and practical to rely solely on the suction pressure (measured in mmHg), which is displayed on all commercially available devices.

During an operative vaginal delivery, practitioners assist by adding to the momentum of the maternal expulsive efforts (unless Valsalva is contraindicated) rather than pulling the fetus out independently. As soon as a contraction starts and the mother begins pushing, the negative pressure is rapidly raised to 500 to 600 mmHg (green zone on the vacuum indicator gauge).

Traction is applied gradually as the contraction builds and is maintained for the duration of the contraction, but only in coordination with the mother's pushing (the number of pulls depends on the number of pushes; there is one "set of pulls" per contraction). Both hands are employed, and work in tandem. The fingertips of the dominant hand pull the device's crossbar, while the nondominant hand monitors the progress of descent and prevents cup detachment by placing counter pressure with the thumb [26]. During the extraction, the stem of the device is kept perpendicular to the plane of the cup to maintain the seal with the fetal head. The device is more likely to detach if angular traction is applied or with pendulum or rocking motions. Jerking the device will lead to unnecessary pop-offs.

Traction is applied along the axis of the pelvic curve to guide the fetal vertex, led by the flexion point, through the birth canal. Initially, the angle of traction is downward (toward the floor); the higher the beginning station, the steeper the angle of downward traction required. The axis of traction is then extended upwards to a 45 degree angle to the floor as the head emerges from the pelvis and crowns. In addition, the handle of the device is allowed to passively turn as the head auto-rotates through its descent. The handle should never be actively twisted to rotate the head. This dangerous maneuver can cause "cookie cutter" injuries to the fetal scalp [27].

Traction is gradually discontinued as the contraction ends or the mother stops pushing. Descent should occur with each application of traction, beginning with the first.

Maintaining versus releasing suction — Between contractions, suction pressure can be fully maintained or reduced to <200 mmHg; it is well established that fetal morbidity is similar for both regimens [28].

When the head is delivered, the suction is released, the cup is removed, and the remainder of the delivery proceeds as usual. (See "Management of normal labor and delivery".)

Episiotomy — We favor non-midline episiotomy in nulliparous patients undergoing vacuum-assisted deliveries. The role of routine episiotomy with vacuum-assisted deliveries to prevent obstetric anal sphincter injuries (OASIS) has not been established due to the absence of randomized trials and limitations of data from observational studies (eg, study did not distinguish between forceps and vacuum delivery, omission of the type of episiotomy performed, confounding by indication). However, available data suggest a benefit from non-midline episiotomy:

●In a meta-analysis of 15 observational studies investigating the risk of OASIS in vacuum-assisted delivery with and without the use of mediolateral or lateral episiotomy in a first vaginal birth, non-midline episiotomy was associated with a reduced risk of OASIS (odds ratio [OR] 0.53, 95% CI 0.37-0.77) [29].

●In a subsequent large retrospective observational study, the incidence of OASIS following vacuum delivery in 130,157 nulliparous patients with and without a mediolateral episiotomy was 2.5 and 14 percent, respectively (adjusted OR 0.14, 95% CI 0.13-0.15); for 29,183 parous patients, the incidence with and without mediolateral episiotomy was 2.0 and 7.5 percent, respectively (adjusted OR 0.23, 95% CI 0.21-0.27) [30].

Rotations — Management of the fetus in posterior or transverse position may involve expectant management, manual rotation, operative vaginal delivery, or cesarean. (See "Occiput posterior position", section on 'Management' and "Occiput transverse position", section on 'Approach to patients with transverse arrest'.)

For a vacuum-assisted delivery:

●Occiput posterior – For the fetus in occiput posterior position, extraction is performed using a vacuum cup designed for the posteriorly positioned occiput and without attempts at rotation. (See 'Occiput posterior position' above.)

●Occiput transverse – For the fetus in occiput transverse position, the handle of the device is allowed to passively rotate as the head auto-rotates from transverse or other off-midline positions to a direct anterior or posterior position as it descends. The handle should never be actively twisted to rotate the head as this dangerous maneuver can cause "cookie cutter" injuries to the fetal scalp [27]. (See "Occiput transverse position", section on 'Forceps rotation'.)

DURATION — The maximum time to safely complete a vacuum-assisted delivery and the number of acceptable "pop-offs" are unknown. A maximum of two to three cup detachments, three sets of pulls for the descent phase, three sets of pulls for the outlet extraction phase, and/or a maximum total vacuum application time of 15 to 30 minutes are often recommended, although most authors advise lower application time limits [23,31-33].

These recommendations are mostly based upon common sense and experience but are supported by two studies assessing the risks associated with cup detachments and duration of the procedure. In both of these studies, the majority of successful vacuum-assisted deliveries was achieved within the duration and detachment parameters recommended, and the risks associated with multiple "pop-offs" (more than three) and/or prolonged procedures (more than 15 to 30 minutes) appear to justify avoiding this type of use in most circumstances, even though the absolute risk of an adverse outcome is low.

●One of these studies reports the findings from a secondary analysis of a multicenter observational cohort of 3594 women who underwent an attempted vacuum delivery and provides insight into the absolute neonatal risks associated with detachment of the vacuum cup and the duration of the procedure [34]. In this study:

•Approximately 60 percent of patients had 0 detachments, 22 percent had 1 detachment, 12 percent had 2 detachments, and 6 percent had ≥3 detachments. The composite adverse neonatal outcome for patients with 0, 1, 2, and ≥3 detachments was 2.4, 3.6, 4.6, and 4.8 percent, respectively. Composite neonatal outcome was defined as any of the following: brachial plexus injury, facial nerve palsy, clavicular fracture, skull fracture, other skeletal fracture, skin laceration, intracranial hemorrhage (including subgaleal hemorrhage [SGH]), seizure requiring treatment, or neonatal death. Skin laceration was the most common individual adverse outcome.

•The duration of vacuum delivery was defined as the time from first application of the vacuum to either time of vaginal birth or time of decision to convert to cesarean. Composite adverse neonatal outcomes for durations of 0 to 2, 3 to 5, 6 to 8, 9 to 11, and ≥12 minutes were 1.1, 2.8, 3.6, 3.7, and 5.0 percent, respectively. In multivariate analysis, increasing duration of vacuum delivery was more predictive of adverse neonatal outcome than an increasing number of detachments.

●The second study, a retrospective analysis of 350 neonates with SGH exposed to vacuum-assisted delivery and 350 matched controls, evaluated the factors associated with SGH formation following attempted vacuum extraction [35]. In this study:

•The odds of SGH expressed as the risk for each cup detachment were 2.38, and three or more cup detachments were independently associated with SGH formation.

•Duration of vacuum delivery ≥15 minutes (defined as the time of first application of the vacuum to vaginal birth) was also independently associated with SGH with an adjusted odds ratio of 2.04 for each three minute increase.

DOCUMENTATION — Documentation should include all of the following:

●The indication for the procedure

●Fetal status (station, position, estimated fetal weight, interpretation of the fetal heart rate tracing)

●A description of the discussion with the patient

●A description of the procedure itself, including:

•Type of anesthesia

•Type of vacuum cup

•Maximum negative pressure achieved

•Total time of negative pressure and whether the negative pressure was reduced between contractions

•Number of pulls and contractions

•Number of detachments

•Description of progress with each pull

•Whether an episiotomy was performed or lacerations occurred

It is also worth documenting that the prerequisites for vacuum delivery were met: cervix fully dilated, maternal bladder empty, and no known fetal contraindications were present (eg, the gestational age was ≥34 weeks, no known fetal bleeding diathesis, etc) and the method used for determining station (eg, +2 of 3 versus +2 of 5).

FAILED PROCEDURES

Causes of failure — The reasons for failure with vacuum-assisted deliveries are multifactorial. The key with an unsuccessful operative procedure is to review the events step-by-step to identify areas for future technique alternations or decision changes.

Some reasons for failure include:

●Fetopelvic disproportion (eg, non-occipitoanterior position, macrosomia, uterine constriction ring).

●Incorrect technique – Pulling the stem too quickly or when maternal expulsive efforts are weak will lead to cup detachments. Moreover, upwards traction before the head is crowning will tend to disrupt the vacuum seal and lead to pop-offs. Incorrect cup size also increases the risk of failure.

●Paramedian or deflexing applications – It is essential to identify the flexion point and focus the vacuum traction to leading the mentovertical diameter through the pelvis. Off-midline applications or deflexing applications will pull less favorable diameters of the fetal head through the pelvis and inhibit, rather than assist, delivery [36].

●Large caput succedaneum – An increase in fetal scalp edema lets more of the scalp to be drawn into the cup, which reduces the available vacuum area, and, in turn, lessens total traction. The effect is more pronounced with bell-shaped cups than in M-style cups [9], and with soft cups compared with rigid cups [8].

Risk factors — In a retrospective case-control study of 306 failed and 618 successful vacuum-assisted deliveries [37]:

Predictors of a failed procedure included:

●Estimated fetal weight ≥3750 g as compared with <3250 g (odds ratio [OR] 5.7)

●Epidural analgesia (OR 3.0)

●Occiput posterior position (OR 2.6)

●Failure to progress as the indication (OR 1.7)

●Labor augmentation (OR 1.4)

●Increasing gestational age (OR 1.2 per week)

Predictors of a successful procedure included:

●At least one previous vaginal birth (OR 0.32)

●Lower station of the fetal head at start of the procedure (OR 0.31 per station more descended)

●Taller maternal height

Potential tools for predicting failure — Using ultrasound to measure the distance from the presenting part of the fetal head to the maternal perineum, and then predicting vacuum delivery success based on this number, is an investigational tool. Head-to-perineum distances >35 mm in one study and >40 mm in another study, which correlated with +2 station, were associated with higher vacuum failure rates and more difficult extractions [38,39].

Another investigational technique uses a combination of the ultrasound-measured angle of progression with pushing (AoP) and fetal head circumference to predict complicated versus uncomplicated operative vaginal deliveries. In this model, a combination of an AoP with pushing of less than 115° and a fetal head circumference greater than 345 mm predicted 87 percent of complicated operative vaginal deliveries [40].

Management after a failed procedure — Prompt cesarean delivery is advised after an unsuccessful vacuum-assisted procedure. Failure of an attempted vacuum-assisted delivery increases the likelihood of neonatal morbidity [41]; the subsequent use of sequential forceps in this setting has been associated with an increased risk of neonatal intracranial hemorrhage [42] and is rarely indicated.

REDUCING THE RISK OF COMPLICATIONS — All operative vaginal deliveries carry some risk of complications, such as intracranial hemorrhage. No studies have clearly demonstrated a benefit of one type of vacuum cup over another for preventing serious complications. Similarly, no threshold for duration of vacuum application or maximum number of pop-offs has been proven to prevent serious complications.

The following tips are useful for reducing the risk of complications:

Confirm correct cup placement — A successful vacuum-assisted delivery requires placement of the cup over the flexion point. Misalignment of the cup relative to the flexion point leads to cranial deflexion or asymmetry as traction is applied, which impedes, rather than assists, the delivery process because a larger cranial diameter is presented to the birth canal. Paramedian application is also associated with a higher rate of neonatal scalp trauma [24].

If the cup is dislodged, the scalp is examined to make sure there is no injury before reapplying the cup.

Avoid entrapping vaginal soft tissues — Entrapment of maternal tissues between the cup and the fetal head will cause vaginal and/or vulvar lacerations, which can be difficult to repair and cause unnecessary maternal blood loss and discomfort.

Know when to abandon the procedure — As with any obstetric intervention, practitioners must be willing and able to abandon the procedure and proceed to cesarean delivery promptly when the vaginal delivery is not progressing normally [43]. Although there is often a tendency to try to complete the delivery vaginally despite failed progress and/or multiple "pop-offs," prudence dictates abdominal delivery when the fetus is not readily delivered with vacuum assistance. An indicated vaginal delivery that could not be completed with vacuum assistance is unlikely to progress to a spontaneous vaginal delivery with a little more time, and delay may increase the risk of neonatal or maternal morbidity. (See 'Duration' above.)

COMPLICATIONS AND OUTCOME — The complications and outcomes of vacuum delivery are discussed separately. (See "Operative vaginal delivery", section on 'Complications'.)

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Delivery".)

SUMMARY AND RECOMMENDATIONS

●There is insufficient evidence upon which to base a recommendation for use of a particular type of vacuum cup (table 1) for all circumstances when a vacuum-assisted delivery is attempted. A successful vacuum extraction is most likely to be achieved by accurate cup application, appropriate traction technique, a favorable flexed fetal cranial position and low station at the time of application, use of the most appropriate cup design, and absence of fetopelvic disproportion. (See 'Extractor cup' above and 'Technique' above.)

●The three major categories of indication are prolonged second stage of labor, nonreassuring fetal status, and shortening the second stage for maternal benefit, but there is no absolute indication. In addition to the general contraindications to operative vaginal delivery, contraindications specific to vacuum extraction include gestational age less than 34 weeks and previous scalp sampling. (See 'Indications and contraindications' above.)

●The cup should be applied at the flexion point and the edges swept with a finger to insure that no maternal tissues are entrapped. In the normally molded fetal head, the flexion point is in the midline, over the sagittal suture, approximately 6 cm from the anterior fontanelle and 3 cm from the posterior fontanelle (figure 1). (See 'Determine the flexion point' above.)

●Rapid application to the maximum suction pressure of 600 mmHg is acceptable, although pressures in excess of 450 mmHg are rarely necessary. Slow, stepwise application of suction does not improve safety or efficacy. Between contractions, suction pressure can be fully maintained or reduced to <200 mmHg. (See 'Rapidly apply suction' above and 'Exert traction during contractions' above.)

●Apply gentle traction along the axis of the pelvic curve (ie, down then up) in concert with maternal pushing. The scalp can be damaged if the handle is actively twisted to rotate the head. A mnemonic is provided in the table (table 2) to assist in remembering the steps in vacuum extraction. (See 'Exert traction during contractions' above.)

●We suggest limiting vacuum-assisted procedures to three contractions for the descent phase, three contractions for the outlet extraction phase, 2 to 3 "pop-offs," and a total time of 15 to 30 minutes (Grade 2C). (See 'Duration' above.)

●Failure of an attempted vacuum-assisted delivery increases the likelihood of neonatal morbidity; the subsequent use of sequential forceps in this setting is rarely indicated. Prompt cesarean delivery is advised after an unsuccessful vacuum-assisted procedure. (See 'Failed procedures' above and 'Know when to abandon the procedure' above.)