Vacuum-assisted vaginal birth: Technique

INTRODUCTION — 

The decision to use an instrument to assist vaginal birth balances the maternal, fetal, and neonatal impact of the procedure against the alternative options of cesarean birth or expectant management. The technique for vacuum-assisted vaginal birth will be reviewed here. An overview of issues related to assisted vaginal birth, including choice of vacuum versus forceps, is available separately. (See "Assisted (operative) vaginal birth: Overview".)

Use of vacuum to help extract the fetus at cesarean birth is also discussed separately. (See "Cesarean birth: Management of the deeply impacted head and the floating head", section on 'Extraction with vacuum, obstetric spoon, or forceps'.)

INDICATIONS AND CONTRAINDICATIONS

Indications — An assisted vaginal birth (vacuum or forceps) should only be attempted when a specific obstetric indication is present [1,2]. The three major categories of indication are:

●Prolonged second stage of labor

●Suspected fetal compromise

●Shortening the second stage for maternal benefit (eg, maternal cardiac or neurologic disease, exhaustion)

These indications are discussed in detail separately. (See "Assisted (operative) vaginal birth: Overview", section on 'Indications'.)

Potential contraindications

●Contraindications specific to vacuum-assisted birth

•Gestational age <34 weeks – Historically, experts have recommended avoiding use of vacuum devices before 34 weeks because the risk of inducing intracranial bleeding was thought to be higher at earlier gestational ages. This perception is supported by a review of Swedish registry data in which the frequency of intracranial hemorrhage in vacuum-assisted births was higher at <34 weeks compared with 34 to 36 weeks (72 in 1000 versus 4 in 1000) and higher than that with intrapartum cesarean at <34 weeks (56 in 1000) or at 34 to 36 weeks (3 in 1000) [3]. While these data were gathered retrospectively and confounded by indication, avoiding vacuum extraction before 34 weeks is a prudent approach. Forceps can be used instead. (See "Assisted (operative) vaginal birth: Overview".)

The American College of Obstetricians and Gynecologists guidance states that "vacuum extraction has been discouraged for gestational age less than 34 weeks, although a safe lower limit for gestational age has not been established" [4].

•Prior fetal scalp trauma – Prior scalp sampling or multiple attempts at fetal scalp electrode placement are relative contraindications to use of vacuum because scalp trauma from a procedure theoretically may increase the risk of cephalohematoma or external bleeding from the scalp wound.

●Contraindications to both vacuum- and forceps-assisted births

•Suspected fetal-pelvic disproportion – This may be related to suspected macrosomia (eg, estimated fetal weight >4500 g) or suspected contracted pelvis (which may be related to congenital, developmental, nutritional, metabolic, or traumatic factors).

•Selected fetal and maternal disorders – Disorders such as 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 assisted vaginal birth because of perceived increased risks of fetal or maternal trauma, but both the absolute and relative risks are poorly defined.

PREDICTORS OF SUCCESS AND RISK FACTORS FOR FAILURE — 

Vacuum-assisted birth is attempted when, in the clinical judgment of the operator, the intervention is indicated and will be successful. However, the outcome cannot always be predicted with certainty. In a retrospective case-control study of 306 failed and 618 successful vacuum-assisted births, predictors of a successful procedure included [8]:

●At least one previous vaginal birth (odds ratio [OR] 0.32)

●Lower station of the fetal head at the start of the procedure (OR 0.31 per station more descended on a -3 to +2 scale)

●Taller maternal height (OR 0.97 per cm)

Predictors of a failed procedure included:

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

●Epidural anesthesia (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)

Investigative 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 chances of procedure success based on this number, is an investigational tool [9,10]. 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 vacuum- or forceps-assisted vaginal births [11]. Although of academic interest, neither tool has a clinical role at this time.

PREREQUISITES — 

The prerequisites and definitions of a vacuum-assisted birth are generally similar to those for a forceps-assisted birth. They are listed below and discussed in more detail separately. (See "Assisted (operative) vaginal birth: Overview", section on 'Prerequisites'.):

●Operator is experienced in vacuum-assisted vaginal birth.

●Cervix is fully dilated.

●Membranes are ruptured.

●Fetal presentation, position, station, and any asynclitism are known.

●Vertex presentation.

●Head is engaged (and ideally the leading point of the skull is ≥2 cm beyond the ischial spines). Caput and molding are noted.

PATIENT COUNSELING — 

The reasons for performing an instrument-assisted vaginal birth and its potential risks are discussed. (See 'Indications' above and 'Adverse events and complications' below.)

The benefits and risks of the alternatives (expectant management, forceps-assisted vaginal birth, or cesarean birth) are also discussed. (See "Assisted (operative) vaginal birth: Overview", section on 'When to choose vacuum versus forceps' and "Assisted (operative) vaginal birth: Overview", section on 'Adverse effects and complications'.)

PATIENT PREPARATION

●Informed consent for the procedure. (See "Informed consent in obstetrics".)

●Adequate anesthesia. Adequate anesthesia can be obtained with a neuraxial technique or with a pudendal/local block. Nitrous oxide alone is inadequate. Vacuum-assisted birth can be attempted without anesthesia if necessary in an emergency, particularly for an outlet vacuum, but the patient will likely experience discomfort. Forceps are not recommended without neuraxial anesthesia or pudendal block. (See "Neuraxial analgesia for labor and delivery (including instrumental delivery)".)

●Bladder empty (via voiding or catheterization).

●Patient in the dorsal lithotomy position.

We do not administer antibiotic prophylaxis prior to or after assisted delivery as no benefit has been established, although data are sparse [12].

EQUIPMENT — 

Equipment consists of a vacuum pump, a cup to attach to the fetal scalp, and a handle attached to the cup by a rigid or nonrigid stem.

Vacuum pump — Suction is usually generated manually, either with a pump integrated into the handle that the operator controls without the need for an assistant (picture 1 and picture 2) or with a separate pump that is engaged by an assistant (picture 3).

Some vacuum devices also come with a traction force indicator, which enables the operator to compare tactile impression with an objective measure of force.

Cup — Vacuum cups may be soft or rigid and the shape may be bell- or "M"-shaped (picture 4). The optimal type of cup to use for each clinical scenario has not been determined as few randomized trials or comparative studies have been performed.

Size — Cup sizes vary somewhat by manufacturer and cup shape, but any of the standard cups may be used for fetuses ≥34 weeks of gestation.

Consistency (soft, rigid) — Soft cups are made of pliable plastic, silicone, rubber, or polyethylene. Rigid cups are made of hard plastic, polyurethane, or polyethylene, although they were originally made of metal.

The performance characteristics of soft versus rigid cups have been examined in numerous trials performed in the 1980s and 1990s. In a meta-analysis of randomized trials comparing soft versus rigid cups [13]:

●Soft cups resulted in less scalp injury (31 versus 48 percent; OR 0.65, 95% CI 0.50-0.80).

●Soft cups were less successful (failed vaginal delivery: 17.4 versus 10.8 percent; risk ratio [RR] 1.62, 95% CI 1.21-2.17).

●Soft cups did not clearly reduce the risk of any maternal trauma (9.4 versus 9.6 percent; OR 0.63, 95% CI 0.24-1.67) or third- or fourth-degree perineal laceration (2.4 versus 2.6 percent; RR 0.93, 95% CI 0.35-2.44).

The trials in the meta-analysis had important limitations, including lack of blinding and selective reporting. These issues limit the certainty of the findings.

Differences in performance between soft versus rigid cups are likely related to cup shape: soft cups are usually bell-shaped while rigid cups tend to be mushroom-shaped (picture 4).

Shape (bell or mushroom) — Conclusive studies comparing the clinical 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 [14].

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. When bell-shaped cups draw the chignon into the cup, the available vacuum space is reduced, leading to a reduction in cup adhesiveness at the edges, which allows leakage of air and eventual detachment. By comparison, when the mushroom-shaped "M"-style cups draw the chignon into the cup, 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 [15,16].

Choice of cup — Several types of cups are available (table 1).

●Occiput anterior position at the vaginal outlet – Soft bell-shaped cups appear to be the most suitable choice since these extractions typically do not require a large amount of traction; thus, there is less chance of cup detachment and, in turn, scalp injury.

●Occiput anterior position in the low- to mid-vagina and occiput transverse position – Rigid bell-shaped or mushroom cups tend to be most suitable for occiput anterior position extractions deeper in the vagina given their ability to stay attached despite strong traction.

●Occiput posterior position – While forceps are preferred for occiput posterior position, providers who do not perform forceps may use vacuum, albeit with a higher failure rate. A rigid mushroom-shaped cup with nonfixed traction cord that inserts parallel to the cup is best for delivery from the occiput posterior position (table 1) because the flexion point of the head is deeper and more posterior in the vagina than with occiput anterior position. A mushroom-shaped cup and a nonfixed traction cord facilitate deep placement in the posterior vagina, whereas the greater height and relatively rigid stem of most bell-shaped cups impede accurate placement in this setting. Furthermore, when traction is applied, a nonfixed traction cord that inserts parallel rather than perpendicular to the cup results in more favorable force vectors to encourage flexion of the fetal head during delivery.

One appropriate-choice device, the Kiwi OmniCup (picture 1), has a unique combined handle/vacuum pump. When considering a vacuum-assisted birth with the Kiwi OmniCup for a patient whose fetus is in the occiput posterior position, clinicians should take into account data suggesting occiput posterior position as independent risk factor for both neonatal subgaleal hemorrhage and maternal anal sphincter injury [17].

●Deflexed head – A rigid mushroom-shaped cup with a nonfixed traction cord is also useful for a deflexed head since the cup needs to be placed deep in the vagina.

CHECKLIST — 

Checklists can be helpful as cognitive aids for ensuring safety and adequate documentation (eg, indication, absence of contraindications, preprocedure maternal and fetal assessments/findings). Checklists have been published by the Society for Maternal Fetal Medicine [18], Royal College of Obstetricians and Gynaecologists [19], and the Society of Obstetricians and Gynaecologists of Canada [20], among others, and can be modified to fit local requirements.

The following table describes the author's suggestions for the basic components of the checklist (table 2).

TECHNIQUE FOR OCCIPUT ANTERIOR POSITION

Confirm fetal position — Confirm preprocedure assessment of fetal position, station, molding, caput, and asynclitism and document findings. Ultrasound examination can be useful if digital examination is uncertain.

Place the cup

●Spread the labia and insert a bell-shaped cup by compressing and placing it into the vagina while angling posteriorly. If an "M"-style or rigid cup is used, flex the cup at the base of the shaft and insert sideways into the vagina while angling posteriorly.

●When the cup is in contact with the fetal head, place its center over the flexion point. The flexion point is where outward traction rotates the head toward a midline position, flexes the neck, and pulls the wide mentovertical occipital diameter along the curve of the birth canal. Failure to place the cup over the flexion point can impede extraction, rather than assist it.  

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). Since most of the commonly used vacuum cups have a diameter between 5 and 7 cm, the edges of the cup should be approximately 3 cm from the anterior fontanelle and at the edge of the posterior fontanelle when the center of the cup is placed over the flexion point. 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.

●Digitally inspect the entire 360° circumference of the cup to ensure 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 confirming correct placement, raise the vacuum pressure to 100 to 150 mmHg to maintain the cup's position. Digitally inspect the edges of the cup again 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 — As soon as a contraction starts and the mother begins pushing, negative pressure is rapidly raised to 500 to 600 mmHg (green zone on the vacuum indicator gauge). Although a slow, stepwise increase in suction over 8 to 10 minutes was recommended in the past, randomized trials have demonstrated that rapid application of negative pressure over one to two minutes reduced the duration of the procedure without compromising effectiveness or safety [21].

Although vacuum suction pressures of 500 mmHg to a maximum of 600 mmHg have been recommended during traction, pressures in excess of 450 mmHg are rarely needed (green zone) (picture 5) [22,23]. Lower suction pressures increase the risk of cup detachment, whereas pressures greater than 600 mmHg increase the risks of fetal scalp trauma and cerebral, cranial, and scalp bleeding. The notion that the vacuum is designed to pop off before damage occurs is erroneous and should not be considered a safety mechanism. (Note: 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)

Exert traction during contractions — Apply traction gradually as the contraction builds and maintain it for the duration of the contraction, 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). Avoid pendulum or rocking motions or jerking the device when applying traction, which will lead to unnecessary detachments.

Use the fingertips of the dominant hand to pull the device's crossbar. Use the fingers of the nondominant hand to monitor the progress of descent and apply counter pressure to the cup to avoid detachment [24].

Keep the stem of the device perpendicular to the plane of the cup to maintain the seal with the fetal head. The cup is more likely to detach if angular traction is applied.

Apply traction 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. 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 as this maneuver can cause "cookie cutter" injuries to the fetal scalp [25].

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.

How much traction? — It is clinically reasonable and practical to rely solely on negative pressure (measured in mmHg), which is displayed on all commercially available devices, as a proxy for traction force.

The absolute "safe" traction force for vacuum extraction is unknown. In 1962, one group determined a total traction force of 17.6 kilogram-force (kgf; 172.6 Newton [N]) was typically necessary to affect delivery [26]. Other authors subsequently determined the traction force to be lower, approximately 12 kgf (117.7 N) in multiparous patients [27-29]. An observational study of 560 vacuum-assisted births using an OmniCup vacuum device with a traction force indicator found that 86 percent of extractions occurred with ≤11.5 kgf (112.8 N) traction and 14 percent with >11.5 kgf (112.8 N) traction [30]. 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 [31].

In the absence of a traction gauge, traction force (measured in kgf or N) can be calculated based on negative pressure, cup size, and altitude. Cup sizes vary among different manufacturers' devices and cup size affects the overall traction force applied since force = (area under the cup)X(negative pressure). Therefore, as cup size increases, the total force applied will rise even with the same amount of negative pressure [32]. As an example, with 600 mmHg of negative pressure, a 50 mm cup will generate 15.7 kgf of traction force while a 60 mm cup will generate 22.6 kgf of traction force. Whether the greater traction forces associated with larger cup sizes are associated with higher vaginal birth rates or more fetal morbidity is unclear.

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 approaches [33].

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

Role of episiotomy — If the operator believes an episiotomy is indicated, we favor nonmidline (mediolateral or lateral) over midline episiotomy to reduce the risk of obstetric anal sphincter injuries (OASIS) [34-36]. Whether an episiotomy is needed and if so, whether to perform a lateral versus midline episiotomy, is based on clinical judgment. A component of this decision is the clinician's assessment of the likelihood of OASIS. (See "Approach to episiotomy", section on 'Median (midline), mediolateral, and lateral episiotomy'.)

In a randomized multisite trial assessing the effect of lateral episiotomy versus no planned episiotomy on obstetric anal sphincter injury (OASIS) in over 700 nulliparous patients undergoing vacuum extraction, a lateral episiotomy reduced the rate of OASIS (6 versus 13 percent, risk difference -7 percent, 95% CI -11.7 to -2.5); RR adjusted for site 0.47, 95% CI 0.23-0.97 [36]. Approximately 14 lateral episiotomies were needed to avoid one OASIS. However, lateral episiotomy also increased the rates of wound infection (9 versus 5 percent; RR 1.96, 95% CI 1.11-3.46) and dehiscence (9 versus 3 percent; RR 2.78, 95% CI 1.45-5.30). Other maternal and neonatal outcomes were not significantly different between groups.

Of note, patients were randomized at the time the decision to perform a vacuum extraction was made and 90 percent of the episiotomy group and 19 percent of the no episiotomy group subsequently had an episiotomy. The lateral episiotomy was begun 1 to 3 cm from the posterior fourchette, at a 60° (45 to 80°) angle from the midline, and was 4 cm (3 to 5 cm) long. The authors plan follow-up to assess long-term pelvic floor function.

One limitation of the trial was basing the diagnosis of OASIS on visual inspection and vaginal and rectal examination of two assessors not blinded to patient allocation and where one assessor was often the same physician who performed the vacuum extraction.

Procedure duration — The maximum time to safely complete a vacuum-assisted birth and the number of acceptable detachments are unknown. Protocols vary but often suggest:

●No more than two or three cup detachments (the manufacturer of the Kiwi vacuum system specifically recommends considering abandoning the procedure after two cup detachments [37])

●No more than three sets of pulls for the descent phase

●No more than two sets of pulls when the scalp is visible through the labia without contractions or pulling

●No more than 30 minutes has transpired from the first pull with the vacuum, although most authors advise a lower application time limit [29,38-40]

These recommendations are based primarily upon common sense and experience, keeping in mind that longer procedures or more cup detachments may be surrogate markers for more difficult extractions. However, they are supported by at least 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 births was achieved within the duration and detachment parameters suggested above, and the risks associated with multiple detachments (more than three) and/or prolonged procedures (more than 15 to 30 minutes) appeared to justify avoiding these practices in most circumstances, even though the absolute risk of an adverse outcome was low.

●The largest of the two studies described the findings from a secondary analysis of a multicenter observational cohort of nearly 3600 patients in whom vacuum-assisted birth was attempted [41]. The findings provide insight into the absolute neonatal risks associated with cup detachment and procedure duration:

•Approximately 60 percent of patients had 0 detachments, 22 percent had 1 detachment, 12 percent had 2 detachments, and 6 percent had ≥3 detachments.

-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.

•Procedure duration was defined as the time from first application of the vacuum to either time of vaginal birth or time of decision to convert to a cesarean.

-Composite adverse neonatal outcome for durations of 0 to 2, 3 to 5, 6 to 8, 9 to 11, and ≥12 minutes was 1.1, 2.8, 3.6, 3.7, and 5.0 percent, respectively. In multivariate analysis, increasing procedure duration was more predictive of adverse neonatal outcome than an increasing number of detachments.

Composite adverse 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), seizure requiring treatment, or neonatal death. Skin laceration was the most common individual adverse outcome.

●The second study of 700 vacuum-assisted births compared 350 neonates with subgaleal hemorrhage with 350 matched controls without subgaleal hemorrhage to evaluate factors associated with subgaleal hemorrhage formation [42].

•Risk of subgaleal hemorrhage more than doubled with cup detachment: for each cup detachment the OR was 2.38, and three or more cup detachments were independently associated with subgaleal hemorrhage formation.

•Procedure duration ≥15 minutes (defined as the time of first application of the vacuum to vaginal birth) was independently associated with subgaleal hemorrhage with an aOR of 2.04 for each three-minute increase.

Although the manufacturer of the Kiwi vacuum system specifically recommends abandoning the procedure after two cup detachments, there is no evidence to support a different stopping threshold for Kiwi versus other vacuum systems.

TECHNIQUE FOR OCCIPUT POSTERIOR OR TRANSVERSE POSITION — 

Management of the fetus in occiput posterior or transverse position may involve expectant management, manual rotation, assisted vaginal birth, or cesarean birth.

(See "Occiput posterior position", section on 'Management' and "Occiput transverse position", section on 'Approach to OT with transverse arrest'.)

For assisted vaginal births in which the fetus is presenting in the occiput posterior or transverse position, we prefer use of forceps over vacuum, given the lower failure rate with forceps and the higher rate of neonatal complications with failed vacuum. When a provider with the requisite forceps skills is not available and a vacuum-assisted birth is planned, the technique is the same as described above for occiput anterior position, with the following exceptions:

●Occiput posterior – A rigid mushroom-shaped cup with nonfixed traction cord that inserts parallel to the cup is best (table 1) without attempts at rotation. (See 'Choice of cup' above.)

●Occiput transverse – A mushroom-shaped cup with a nonfixed traction cord should be used for rotational vacuum deliveries. 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 under traction. The handle should never be actively twisted to rotate the head as this dangerous maneuver can cause "cookie cutter" injuries to the fetal scalp [25]. (See "Occiput transverse position", section on 'Forceps rotation'.)

DOCUMENTATION — 

Documentation of a vacuum-assisted birth generally includes all of the following:

●The indication for the procedure

●Fetal status (station [on a scale of 3 or 5 cm], position, estimated fetal weight, interpretation of the fetal heart rate tracing)

●A description of the discussion with the patient. Obtain written procedural consent signed by the patient when time allows.

●Documentation that the prerequisites for vacuum-assisted birth were met: cervix fully dilated, maternal bladder empty, and absence of known fetal contraindications (eg, the gestational age was ≥34 weeks, no known fetal bleeding diathesis)

●A description of the procedure itself, including:

•Preparation: patient positioning, bladder drainage

•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 and type

•Type and occurrence of lacerations

FAILED PROCEDURES

Causes of failure — After an unsuccessful procedure, it is important to conduct a step-by-step review of events to identify areas for future modification of technique or decision-making. The reasons for failure are multifactorial, and include:

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

●Poor technique – Poor technique can result in cup detachment and a failed procedure. Examples of poor techniques include:

•Choosing the wrong cup (eg, suboptimal size, shape).

•Poor cup placement. 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 [43,44].

•Exerting traction in a jerking rather than gradual manner.

•Exerting traction when maternal expulsive efforts are weak.

•Exerting upward traction before the head is crowning.

●Large caput succedaneum – An increase in fetal scalp edema allows 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 [14], and with soft cups compared with rigid cups [45].

Management after a failed procedure — We suggest cesarean birth within 60 minutes of beginning an unsuccessful vacuum-assisted procedure. Prompt cesarean birth is particularly important if the indication for vacuum-assisted birth was concern about fetal status. Failure of an attempted vacuum-assisted birth increases the likelihood of neonatal morbidity [46]; the subsequent use of sequential forceps in this setting has been associated with an increased risk of neonatal intracranial hemorrhage [47] and is rarely indicated. These data are reviewed separately. (See "Assisted (operative) vaginal birth: Overview", section on 'Second attempt with a different instrument'.)

ADVERSE EVENTS AND COMPLICATIONS

Neonatal — Torsion and traction by the vacuum cup can cause life-threatening neonatal complications, including intracranial hemorrhage (eg, epidural, subdural, intraparenchymal, subarachnoid, intraventricular, subgaleal) (figure 2). Other potential complications include skull fracture, seizures, serious fetal scalp abrasions and lacerations, cephalohematoma, retinal hemorrhage, brachial plexus injury, and death [30,47-51]. (See "Neonatal birth injuries".)

Four complications that appear to occur more often in vacuum-assisted births are:

●Retinal hemorrhage (vacuum: 75 percent, spontaneous vaginal: 33 percent, cesarean: 7 percent [52]). These hemorrhages typically resolve without sequelae within four weeks of birth.

●Subgaleal hemorrhage (vacuum: 0.25 percent, forceps: 0.09 percent, spontaneous vaginal: 0.004 percent [51]).

●Cephalohematoma (vacuum: 9.5 percent, forceps: 3.7 percent [13]). The majority of cephalohematomas resolve spontaneously over the course of a few weeks without any intervention.

●Shoulder dystocia (vacuum: 3.5 percent, forceps 1.5 percent [53], vacuum: 1.1 percent, forceps: 0.54 percent [54]). For this reason, vacuum-assisted births are at higher risk of brachial plexus injury than forceps-assisted or cesarean births [50].

Additionally, a prospective study of vacuum-assisted births found that an increasing number of pulls and prolonged traction were associated with subgaleal hemorrhage [44]. Suboptimal cup placement was associated with failed procedures but not with subgaleal hemorrhage or other vacuum-related birth trauma; however, the small number of events precludes making a clear conclusion about the risk of these latter outcomes.

Maternal — The major maternal risk from assisted vaginal births is genital trauma (eg, third- or fourth-degree perineal laceration, cervical laceration, high vaginal laceration, urethral or bladder injury) [51]. Randomized trials generally report less genital trauma with vacuum compared with forceps extraction (OR 0.65, 95% CI 0.42-1.02), which is not unexpected given that a correctly applied vacuum cup does not take up additional space between the fetal head and the birth canal and does not make contact with maternal soft tissue [13]. However, the difference in rate of genital trauma has not been proven to impact long-term maternal outcomes, such as urinary and anal dysfunction and pelvic organ prolapse.

●In a trial that randomly assigned 75 patients to forceps- or vacuum-assisted birth and then surveyed them five years postpartum, long-term morbidity rates were similar for both instruments; 47 percent had some degree of urinary incontinence and 20 percent had loss of bowel control "sometimes" or "frequently" [55]. This trial was limited by the small number of subjects.

●In a prospective study including over 2100 subjects that used multivariable logistic regression and propensity score methods to control for indication bias, the risk of urinary or anal incontinence at six months postpartum was similar for attempted forceps-/spatula- and vacuum-assisted births [56].

Vacuum-assisted births have been associated with lower rates of maternal morbidity and mortality than cesarean births in the second stage [57]. (See "Fecal and anal incontinence associated with pregnancy and childbirth: Counseling, evaluation, and management" and "Effect of pregnancy and childbirth on urinary incontinence and pelvic organ prolapse".)

TIPS FOR REDUCING THE RISK OF ADVERSE EVENTS AND COMPLICATIONS — 

All assisted vaginal births carry some risk of potentially serious complications. No studies have clearly demonstrated a benefit of one type of vacuum cup over another for reducing these complications. Similarly, no threshold for duration of vacuum application or maximum number of detachments has been proven to prevent serious complications.

The following tips can reduce the risk of complications:

●Comply with professional society guidelines – In a retrospective study, compliance with the Royal Australian and New Zealand College of Obstetricians and Gynaecologists' guidance on instrumental vaginal birth was associated with lower rates of subgaleal hemorrhage (0 versus 11 percent) and major birth trauma (3 versus 22 percent) compared with noncompliance [58]. The main deviation from compliance was pulling more than three times.

●Repeatedly confirm correct cup placement – The need for correct cup placement cannot be overstated. A successful vacuum-assisted birth 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, descent because a larger cranial diameter is presented to the birth canal. Paramedian application is also associated with a higher rate of neonatal scalp trauma [30].

If the cup is dislodged, examine the scalp for any injury before reapplying the cup. The cup should not be placed over an injured scalp.

●Repeatedly confirm that vaginal soft tissues are not trapped under the cup – 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, operators must be willing and able to abandon the procedure and proceed to cesarean birth promptly when the vaginal birth is not progressing normally [59]. Although there is often a tendency to try to complete a vaginal birth despite failed progress and/or multiple detachments, prudence dictates moving on to an abdominal birth when the fetus is not readily delivered with vacuum assistance. An indicated vacuum-assisted vaginal birth that could not be completed is unlikely to progress to a spontaneous vaginal birth with a little more time, and delay may increase the risk of neonatal or maternal morbidity. (See 'Procedure duration' above.)

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: Childbirth".)

SUMMARY AND RECOMMENDATIONS

●Indications and contraindications – The three major categories of indication are prolonged second stage of labor, nonreassuring fetal status, and shortening the second stage for maternal benefit. In addition to the general contraindications to assisted vaginal birth, contraindications specific to vacuum extraction include gestational age <34 weeks and previous scalp injury/sampling. (See 'Indications and contraindications' above.)

●Choice of cup – The choice of cup (table 1) is guided by the position and station of the fetal head. Soft cups perform less well than rigid cups because they are more likely to detach, but they have the advantage of being less likely to cause scalp injury; therefore, soft cups the preferred for births that are likely to be successful with lower levels of traction (see 'Choice of cup' above):

•For occiput anterior position at the vaginal outlet, we suggest a soft bell-shaped cup (Grade 2C).

•For occiput anterior position in the low to mid vagina, occiput transverse position, occiput posterior position, or a deflexed head, we suggest a rigid bell-shaped or mushroom cup with a nonfixed traction cord (Grade 2C). For occiput posterior position, a parallel cord insertion is best.

●Technique

•Cup placement – The cup is applied at the flexion point and the edges swept with a finger to ensure 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 'Place the cup' above.)

•Vacuum pressure – 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.)

•Traction – Apply gentle traction along the axis of the pelvic curve (ie, down then up) during maternal pushing. The scalp can be damaged if the handle is actively twisted to rotate the head. A mnemonic to assist in remembering the steps in vacuum extraction is provided in the table (table 3). (See 'Exert traction during contractions' above.)

●Failed procedures – Failure of an attempted vacuum-assisted vaginal birth increases the likelihood of neonatal morbidity. (See 'Failed procedures' above.)

•Definition of failure – There is no standard definition of a failed vacuum-assisted birth and protocols for abandoning the procedure vary. We consider the procedure to be unsuccessful and do not apply more traction if any of the following occur (See 'Procedure duration' above.):

-Two or three cup detachments ("pop-offs")

-Lack of descent despite three sets of pulls for the descent phase

-Lack of extraction despite two sets of pulls when the scalp is visible through the labia without contractions or pulling

-Total vacuum application time no more than 30 minutes

•Management after a failed procedure – If the vacuum-assisted procedure is unsuccessful, prompt cesarean birth (within 60 minutes) is the appropriate next step in most cases since the subsequent use of forceps in this setting increases the risk of neonatal intracranial hemorrhage. This is discussed separately. (See "Assisted (operative) vaginal birth: Overview", section on 'Second attempt with a different instrument'.)