Clinical overview
Assisted (operative) vaginal birth — delivery of the fetus with forceps or a vacuum (ventouse) — is one of the defining technical skills of the obstetrician. Roughly one in ten births in many settings is assisted vaginally, and the safe, judicious use of these instruments shortens the second stage when continuing to await spontaneous birth would expose mother or fetus to harm, while avoiding a second-stage caesarean with its substantially higher maternal morbidity. The choice is rarely "instrument versus nothing"; it is "instrument now versus caesarean now", and a competent registrar must be able to reason through that decision under time pressure, select the correct instrument, place it correctly, and — critically — know when to stop.
In the South African context this skill is sharpened by resource realities. Second-stage caesarean in a district hospital, often at night with a junior on call, carries real risks of impacted fetal head, extension tears, haemorrhage and delay to theatre. A correctly performed assisted vaginal birth in a woman who fulfils the prerequisites can be the safer option — but only where the operator is trained and the conditions are met. The Saving Mothers (NCCEMD) reports repeatedly highlight that inappropriate or failed instrumental delivery, and delays in escalating to caesarean, contribute to avoidable maternal and perinatal harm. The instrument is only as safe as the judgement behind it. This chapter discusses indications, classification, technique, the three instruments named in the objective (forceps, vacuum, and the newer Odon device), and the framework for safe decision-making. See also complicated-labour, perineal-protection and oasis.
Core knowledge
Indications
Indications are conventionally grouped, but in practice they overlap and a single judgement integrates them:
- Fetal: a suspicious or pathological CTG in the second stage, or other evidence of fetal compromise where expedited birth is warranted (see ctg-interpretation and fetal-monitoring-methods).
- Maternal: maternal exhaustion, the need to avoid prolonged Valsalva (e.g. significant cardiac disease, severe hypertension/pre-eclampsia where a controlled second stage is desirable — see pre-eclampsia-and-hellp), or a prolonged second stage.
- Inadequate progress in the second stage: definitions of "prolonged" classically allow longer with regional analgesia and for nulliparous women than for multiparous women; standard teaching (and RCOG GTG 26) uses thresholds in the order of active pushing for ~2 hours (nulliparous) or ~1 hour (multiparous), extended further if epidural analgesia is in place. Use local NDoH/unit thresholds.
There is no absolute numerical indication; the decision is clinical. An assisted birth is appropriate only when the benefit of expediting delivery outweighs the risk of the procedure, and when the prerequisites for a safe attempt are met.
The prerequisites — a non-negotiable checklist
Before any attempt, every condition below must be satisfied. A useful structured mnemonic is the components of a full assessment — many units teach a checklist covering the mother, fetus and operator. The essentials:
- Fully dilated cervix (second stage). Instrumental delivery at less than full dilatation is contraindicated outside very specific circumstances.
- Membranes ruptured.
- Vertex (cephalic) presentation with the position and station precisely known by abdominal and vaginal examination. The operator must know exactly where the occiput is and how much caput/moulding is present.
- Engaged head with no more than one-fifth palpable abdominally; the bony station must be at or below the ischial spines (station 0 or lower). A head that is two-fifths or more palpable abdominally is a contraindication.
- Empty bladder (catheterise).
- Adequate analgesia appropriate to the procedure — at minimum effective perineal/pudendal block for low-cavity lift-outs; regional or denser block for rotational or mid-cavity births.
- Adequate maternal pelvis with no suspicion of cephalopelvic disproportion.
- Consent obtained (verbal in the acute setting, documented), the operator trained and competent for the chosen procedure and station, and a clear plan including where the birth will occur and what to do if it fails (see informed-consent).
- Backup available: ability to proceed to caesarean and neonatal resuscitation standing by (see neonatal-resuscitation).
Classification by station and rotation
The internationally used classification (RCOG GTG 26; ACOG) stratifies by how high the head is and how much rotation is needed — this directly determines difficulty, risk and who should perform it:
| Class | Station / criteria | Rotation |
|---|---|---|
| Outlet | Scalp visible without parting labia; skull on pelvic floor; sagittal suture in AP or ≤45° | ≤45° |
| Low | Leading point of skull at station +2 cm or lower, but not on the pelvic floor | Subdivided: ≤45° vs >45° rotation |
| Mid | Head ≤1/5 palpable abdominally; leading point above +2 but at/below spines | Often >45° rotation |
| High | Not engaged (≥2/5 palpable) | — |
Mid-cavity and rotational births are advanced procedures that should be performed by an experienced operator, often as a trial in theatre with immediate recourse to caesarean. High-cavity instrumental delivery (unengaged head) is contraindicated — proceed to caesarean.
Figure J8.1 — Safety gate for assisted vaginal birth: indications, prerequisites, station classification and the high-head stop rule.
The instruments
Forceps are paired blades (e.g. Neville-Barnes/Simpson-type for non-rotational use; Kielland's for rotation) with a cephalic curve fitting the fetal head and a pelvic curve fitting the maternal pelvis. They grip the head and apply traction (and, with Kielland's, rotation). Forceps deliver a higher proportion of attempts successfully than the vacuum, do not depend on maternal effort, can be used when there is fetal coagulopathy concern over scalp trauma, and give a more controlled head. The trade-off is a higher rate of maternal genital-tract trauma, including third- and fourth-degree (OASIS) tears (see oasis and perineal-protection).
Vacuum / ventouse applies a cup (rigid metal, or soft/flexible silastic, or a hand-held disposable device such as the Kiwi OmniCup) to the fetal scalp over the flexion point (on the sagittal suture, ~3 cm anterior to the posterior fontanelle / ~6 cm from the anterior fontanelle). Suction creates a chignon; traction is applied with maternal effort and during contractions, along the pelvic axis. Compared with forceps the vacuum causes less maternal trauma but is more likely to fail, more likely to cause cephalhaematoma and retinal haemorrhage, and is associated with the rare but serious subgaleal (subaponeurotic) haemorrhage. Vacuum is generally avoided below ~34 weeks (risk of cephalhaematoma/intracranial bleeding) and contraindicated where the fetus has a bleeding diathesis or where face/brow presentation exists.
The Odon device is a newer instrument designed to reduce the trauma and the skill barrier of conventional assisted birth, particularly for low-resource settings. It uses a soft polyethylene sleeve/air-cuff that is positioned around the fetal head with an applicator; inflation of the cuff grips the head circumferentially and traction is then applied, avoiding rigid metal blades or scalp suction. WHO has supported development of the device with the explicit aim of a simpler, safer assisted-birth tool deployable where forceps/vacuum expertise is scarce. It is not yet in routine clinical use: evidence is from early feasibility and clinical investigation rather than from large trials demonstrating equivalence or superiority for fetal/maternal outcomes, and it is not part of standard SA or RCOG practice. Registrars should be able to discuss its rationale (lower training threshold, potential to reduce caesarean and traumatic-birth morbidity globally) while being clear that it remains investigational and that any specific performance claims are not yet established — treat exam answers on the Odon device as conceptual, not as established standard of care.
Table J8.2 — Forceps, vacuum and Odon device compared by mechanism, use case and key trade-offs.
Assessment
The assessment immediately before an assisted birth is itself the safety mechanism. Work systematically:
Maternal and labour assessment
- Confirm the indication and that it is genuine and current (re-read the CTG; reassess maternal condition).
- Confirm full dilatation and ruptured membranes.
- Review the partogram (see partogram-use): how long has the second stage been, what analgesia is in place, is there a record of disproportion or arrest?
- Bladder: empty by catheter.
- Analgesia: confirm adequacy for the planned procedure.
Fetal assessment — the crux
- Abdominal palpation: how many fifths of head are palpable? ≥2/5 = not engaged = do not attempt.
- Vaginal examination: determine position (locate the posterior fontanelle/sagittal suture; identify occiput-anterior, -transverse, or -posterior), station relative to the ischial spines, and the degree of caput (scalp oedema, can mislead the station upward) and moulding (overlapping skull bones — graded; severe moulding (e.g. 3+/bones overlapping and not reducible) signals disproportion and should prompt caution or caesarean).
- Beware the trap of a high station masked by caput and moulding: a head that feels low at the introitus because of a large caput may have its bony part still high. This is a classic cause of failed/traumatic instrumental delivery and of impacted head at caesarean.
Operator and environment assessment
- Is the operator competent for this station and rotation? A registrar early in training should not attempt rotational or mid-cavity births unsupervised.
- Is this a straightforward outlet/low birth on the delivery bed, or should it be a trial in theatre (mid-cavity, rotational, or any doubt) with the team and anaesthetist ready to convert to caesarean within the same setting?
- Is neonatal resuscitation available?
The level-of-care principle applies: at district level, straightforward low/outlet assisted births by a competent generalist are appropriate; mid-cavity/rotational births and any case of doubt belong where caesarean and neonatal support are immediately available, with timely referral when they are not.
Management
The procedure — generic safe sequence
- Prepare: position the woman (lithotomy for forceps/most assisted births), clean and drape, catheterise, confirm analgesia, brief the team and the woman, and have neonatal resus ready.
- Recheck position, station and fifths palpable immediately before applying the instrument.
- Apply the chosen instrument correctly:
- Vacuum: place the cup centred over the flexion point on the sagittal suture; sweep a finger around the cup rim to ensure no maternal tissue is trapped; build suction (to the device's working pressure); apply traction only with contractions and maternal pushing, directing along the pelvic curve (down then up — the "J" of the birth canal).
- Forceps: apply the left blade then the right, articulate, and check the application (sagittal suture midline and perpendicular to the shanks, posterior fontanelle roughly one finger-breadth above the shanks, equal amounts of fenestration palpable on each side, lambdoid sutures equidistant); apply traction with contractions along the pelvic axis.
- Traction discipline: traction is intermittent, synchronised with contractions and pushing, and should produce descent with each pull. If there is no descent, abandon.
- Episiotomy: consider a (usually mediolateral) episiotomy when indicated to protect the perineum, though routine episiotomy is not mandatory — judge per case (see perineal-protection).
- Deliver the head in a controlled fashion, then the body; clamp the cord per delayed-cord-clamping practice if the baby is well.
The stopping rules — know these cold
An assisted vaginal birth that is not progressing is a failed procedure, and persistence causes harm. Abandon and reassess (proceed to caesarean) if:
- No descent with each pull / no progress after the agreed number of pulls (standard teaching limits an attempt to roughly three pulls/contractions with descent, and total application time short — do not grind on).
- The vacuum cup detaches repeatedly (classically, stop after about three "pop-offs") — repeated detachment means malposition, malplacement, or disproportion.
- Birth is not imminent within a reasonable, pre-agreed time/number of pulls.
- Excessive force would be required.
Do not use two instruments sequentially as a matter of routine. Sequential use of vacuum then forceps (or vice versa) markedly increases neonatal trauma (including intracranial injury) and should be avoided; if the first appropriately-applied instrument fails, the default is caesarean, and a decision to use a second instrument must be a deliberate senior judgement, not a reflex.
Failed instrumental delivery and the trial in theatre
For any mid-cavity, rotational, or doubtful case, conduct the attempt as a trial of instrumental delivery in theatre: the woman is prepared for caesarean, regional anaesthesia is in place, the surgical team is scrubbed or immediately available, so that if the trial fails, caesarean proceeds without delay. The feared complication of failed second-stage instrumental birth is the impacted fetal head at caesarean, which causes extension tears, haemorrhage and fetal trauma — anticipate it, and have a plan (e.g. an assistant to push the head up vaginally, reverse-breech extraction, or a uterine relaxant). This is exactly the scenario the Saving Mothers reports flag as avoidable when escalation is timely and operators are trained.
Figure J8.3 — Stopping rules, theatre-trial escalation and post-birth checks after assisted vaginal birth.
After the birth
- Examine the genital tract systematically for tears, including a per-rectal examination to exclude OASIS (see oasis); repair appropriately.
- Document the indication, prerequisites confirmed, classification (station/rotation), instrument(s), number of pulls, ease, any cup detachments, the time, the personnel, and the neonatal condition (Apgars, cord gases where available).
- Examine the neonate and counsel on warning signs: parents and postnatal staff should watch for an enlarging boggy scalp swelling, pallor or floppiness (subgaleal haemorrhage after vacuum is rare but life-threatening), and the baby should be observed accordingly.
- Debrief the mother: explain what happened and why, the implications for future births (most women can have a normal birth subsequently), and offer postnatal review (see respectful-care and normal-puerperium).
South African / NDoH context
- The NDoH National Integrated Maternal and Perinatal Care Guideline (NDoH, 2024) is the SA source of truth for level-appropriate intrapartum care and referral; assisted vaginal birth should be performed by a competent operator with the prerequisites met, and difficult/rotational cases or any uncertainty should be managed where caesarean and neonatal resuscitation are available — refer in good time where they are not.
- HIV: with effective ART and viral suppression there is no specific contraindication to assisted vaginal birth on HIV grounds; standard infection-control and the principle of avoiding unnecessary scalp trauma apply, and ART/PMTCT continues per the SA HIV/ART Consolidated Guidelines (TLD first-line). See hiv-in-pregnancy.
- Resource framing: the relevant comparison in many SA units is a correctly performed, well-indicated assisted birth versus a late, difficult second-stage caesarean — the former is frequently the safer option when prerequisites and competence are present, which is precisely why training in forceps and vacuum must be preserved rather than allowed to atrophy.
Red flags / pitfalls
- Attempting with an unengaged head (≥2/5 palpable / station above the spines). This is contraindicated — proceed to caesarean.
- Being misled by caput and moulding into thinking the head is lower than its bony station; severe, irreducible moulding signals disproportion.
- Ignoring the stopping rules — grinding on past three pulls without descent, or beyond ~3 vacuum pop-offs, causes serious fetal and maternal injury.
- Sequential instruments (vacuum then forceps) as a routine — markedly increases neonatal intracranial trauma; default to caesarean if the correctly-applied first instrument fails.
- Wrong cup placement (off the flexion point, over the anterior fontanelle, or trapping maternal tissue) — causes deflexion, failure and trauma.
- Vacuum in the preterm fetus (avoid below ~34 weeks) or in suspected fetal bleeding diathesis.
- Failing to do a per-rectal examination after delivery and missing an OASIS.
- Missing subgaleal haemorrhage after vacuum — a rare but potentially fatal neonatal emergency; ensure observation and parental warning.
- Performing a mid-cavity/rotational birth on the delivery bed instead of as a trial in theatre, with no immediate route to caesarean.
- Inadequate analgesia, full bladder, or unconfirmed full dilatation — basic prerequisite failures that cause failed/painful/traumatic attempts.
- Treating the Odon device as established practice — it is investigational; do not state performance claims as fact.
Evidence anchors
- RCOG Green-top Guideline No. 26 — Assisted Vaginal Birth. The primary reference for indications, prerequisites, classification by station/rotation, technique, stopping rules and avoidance of sequential instruments.
- RCOG Green-top Guideline No. 29 — Third- and Fourth-degree Perineal Tears (OASIS) — relevant to the heightened trauma risk of forceps and to post-delivery assessment.
- RCOG Green-top Guideline No. 42 — Shoulder Dystocia — a recognised sequela that the operator must anticipate when assisting a difficult or macrosomic birth.
- NICE NG235 — Intrapartum care (2023) and NICE NG229 — Fetal monitoring in labour (2022) — for second-stage management and the fetal indications that drive assisted birth.
- SA NDoH National Integrated Maternal and Perinatal Care Guideline (NDoH, 2024) — the South African source of truth for level-of-care, referral and intrapartum practice.
- Saving Mothers / NCCEMD (latest triennium) — identifies failed/inappropriate instrumental delivery and delayed escalation among avoidable factors in SA maternal morbidity and mortality.
- WHO has supported development of the Odon device as a simplified assisted-birth tool for lower-resource settings; note that, at the time of writing, its evidence base is early/feasibility-stage and it is not in routine use — discuss conceptually only.
Author's note: specific numeric thresholds in this chapter (second-stage time limits ~1–2 h, ~3 pulls, ~3 vacuum detachments, ≤45° rotation cut-offs, station +2 cm, avoiding vacuum below ~34 weeks, flexion-point distances) reflect standard teaching consistent with RCOG GTG 26; exact figures should be confirmed against the current GTG 26 and local NDoH/unit protocols before quoting in an exam. Forceps/vacuum instrument names are illustrative of types, not endorsements. Odon-device claims are deliberately hedged as investigational.