Assisted Vaginal Birth
Overview
In the UK, 10–15% of births are assisted vaginal births (AVB), rising to almost 1 in 3 nulliparous women. The guideline covers vacuum (ventouse) and forceps birth, non-rotational and rotational, and the governance context created by the Montgomery consent ruling and cases of gross-negligence manslaughter following traumatic birth injury.
Classification (Table 1)
- Outlet: scalp visible at the introitus without separating the labia, skull has reached the perineum, rotation ≤45°.
- Low: leading point at station +2 cm but not on the perineum (non-rotational ≤45° / rotational >45°).
- Mid: head ≤1/5 palpable abdominally, leading point at station 0 or +1 cm (non-rotational ≤45° / rotational >45°).
Indications (Table 2)
- Fetal: suspected compromise — pathological CTG, abnormal fetal blood sample, thick meconium.
- Maternal: nulliparous — no continuing progress after 3 hours (active + passive second stage) with regional analgesia, or 2 hours without; parous — 2 hours with regional analgesia, or 1 hour without; maternal exhaustion/distress; medical conditions where Valsalva should be avoided (e.g. cardiac disease, hypertensive crisis, cerebral vascular disease, myasthenia gravis, spinal cord injury).
- No indication is absolute — clinical judgement is required, and the threshold to intervene is lower where several factors coexist. Lack of progress in the first stage is not an indication (cervix must be fully dilated). Forceps/vacuum are contraindicated before full dilatation; vacuum is contraindicated with a face presentation; forceps can be used for the after-coming head of the breech.
Prerequisites — Safety Criteria (Table 3)
- Full abdominal + vaginal exam: head ≤1/5 palpable per abdomen; cervix fully dilated, membranes ruptured; station at or below the ischial spines; fetal head position determined; caput/moulding no more than moderate; pelvis adequate.
- Preparation of mother: informed consent documented; trust and cooperation established; appropriate analgesia (regional for midpelvic/rotational birth); bladder empty, catheter/balloon removed; aseptic technique.
- Preparation of staff: skilled, experienced operator; equipment, bed, lighting and theatre access available; backup plan for midpelvic births (theatre on standby, senior obstetrician present if trainee-led); anticipation of complications (shoulder dystocia, perineal trauma, PPH); staff trained in neonatal resuscitation present. (A "FORCEPS"-style checklist mnemonic covering these same elements — Fully dilated, Occiput position known, Ruptured membranes, Consent/Contractions adequate, Engaged head/Epidural, Pelvis adequate, Sphincter/bladder empty — is a widely used teaching aid built on this table, though it does not appear verbatim in the RCOG text.)
Ventouse vs Forceps
Per the guideline's Cochrane-based comparison (10 trials, 2,923 women, Table 4): vacuum is more likely to fail to achieve vaginal birth (OR 1.7) and is associated with more cephalhaematoma (OR 2.4), retinal haemorrhage (OR 2.0) and maternal worry about the baby (OR 2.2); vacuum is less likely to cause significant maternal perineal/vaginal trauma (OR 0.4), with no significant difference in caesarean rate, low Apgar scores, or need for phototherapy. Soft (silicone) cups fail more often than rigid cups but cause less neonatal scalp trauma. Vacuum failure rates across individual RCTs ranged roughly 17–36% depending on cup type; forceps generally have lower failure but higher maternal trauma rates. Sequential use of instruments increases neonatal and maternal trauma (e.g. OASI 17.4% with sequential instruments vs 8.4% with forceps alone in one UK cohort) and should be avoided by inexperienced operators. Kielland's rotational forceps are less likely to fail and cause less neonatal trauma than rotational vacuum but carry a specific (rare) risk of cervical spine injury and require expert use.
Complications (indicative ranges, RCOG Consent Advice No. 11)
Episiotomy: vacuum 50–60%, forceps ≥90%. Significant vulvovaginal tear: vacuum ~10%, forceps ~20%. OASI: vacuum 1–4%, forceps 8–12%. PPH: 10–40% (both). Cephalhaematoma (mainly vacuum): 1–12%. Retinal haemorrhage (more with vacuum): 17–38%. Subgaleal haemorrhage (mainly vacuum): 3–6 per 1,000. Intracranial haemorrhage (both): 5–15 per 10,000. Cervical spine injury and facial nerve palsy: rare, associated mainly with Kielland's forceps and forceps respectively. Fetal death: very rare. Vacuum should be avoided below 32 weeks and used with caution 32+0–36+6 weeks due to susceptibility to scalp trauma, cephalhaematoma, and jaundice.
Failure and Discontinuation
Risk factors for failed AVB: maternal BMI >30, short stature, estimated fetal weight >4 kg, fetal head circumference above the 95th centile, occipito-posterior position, and midpelvic birth. Vacuum should be discontinued after two "pop-offs" or if there is no progressive descent with correctly applied traction over a maximum of three pulls to the perineum (plus up to three more to complete birth). Forceps should be discontinued if the blades cannot be applied or the handles do not approximate easily, if there is no progressive descent with the first one to two pulls, or if birth is not imminent after three pulls by an experienced operator.
High-Yield Exam Points
- Cervix fully dilated + membranes ruptured is an absolute prerequisite; "failure to progress" in the first stage is never an indication for AVB.
- Vacuum vs forceps trade-off: vacuum fails more but causes less maternal trauma; forceps completes birth more reliably but causes more trauma — pick the instrument to the clinical circumstance and operator skill, not by default.
- Vacuum is contraindicated below 32 weeks and used cautiously 32–36+6 weeks; it is also contraindicated with face presentation.
- Sequential instrument use significantly raises OASI and intracranial haemorrhage risk — avoid unless the balance of risks favours it over caesarean, and never as an inexperienced operator without supervision.
- An experienced operator competent at midpelvic birth must be present from the outset for any rotational or midpelvic attempt; written consent is required for a trial of AVB in theatre.
- Ultrasound assessment of fetal head position is more reliable than digital exam alone and is recommended where there is diagnostic uncertainty.
Source: RCOG Green-top Guideline No. 26 (4th edition published April 2020 (Murphy DJ, Strachan BK, Bahl R; BJOG 2020;127:e70–e112); reviewed September 2024 and validity extended a further two years (next full review due 2026))
Read the original on rcog.org.uk
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