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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- Indications: presumed fetal compromise in 2nd stage, delay in 2nd stage, maternal exhaustion, or medical conditions contraindicating pushing
- Prerequisites (mnemonic): fully dilated cervix, known presentation and position, head ≤1/5 palpable abdominally, adequate analgesia, empty bladder, ruptured membranes
- Ventouse: less maternal trauma but higher failure rate. Cannot use <34 weeks or with face presentation
- Forceps: lower failure rate but higher maternal perineal trauma. Can rotate (Kielland's) or deliver directly (Neville Barnes, Wrigley's)
- Episiotomy often performed — mediolateral in the UK (reduces risk of 3rd/4th degree tears vs midline)
- Trial of instrumental: attempted in theatre with immediate CS available if fails
Overview
Instrumental delivery (also called operative vaginal delivery or assisted vaginal birth) involves the use of forceps or a vacuum extractor (ventouse) to assist delivery of the fetal head. It accounts for approximately 10–12% of all births in the UK. The decision to perform an instrumental delivery requires careful assessment of prerequisites, informed consent, and appropriate expertise. A failed instrumental delivery may necessitate emergency caesarean section, so a clear plan should be in place before attempting.
Epidemiology
Instrumental delivery rates in the UK are approximately 10–12%, though there is significant regional variation. Rates are higher in nulliparous women and those with epidural analgesia. Ventouse is used more commonly than forceps in overall practice, though forceps remain preferred for rotational deliveries and when ventouse has failed. Maternal perineal trauma, particularly obstetric anal sphincter injuries (OASIS), is more common with forceps than ventouse.
Clinical Features
Symptoms
Delay in second stage of labour despite adequate contractions and pushing
Maternal exhaustion preventing effective pushing
Maternal medical condition requiring shortened second stage (e.g., cardiac disease)
Signs
Full cervical dilatation confirmed on vaginal examination
Fetal head at or below the ischial spines (station 0 or below)
Head ≤1/5 palpable abdominally
Pathological CTG in second stage (fetal compromise)
Investigations
First-line
Vaginal examinationConfirm full dilatation, position and station of head, degree of moulding and caput
Abdominal palpationHead must be ≤1/5 palpable abdominally — if >1/5, instrumental delivery is contraindicated
CTGAssess fetal wellbeing — may be the indication for expedited delivery
Second-line
Fetal blood samplingIf CTG pathological and delivery not imminent — pH <7.20 = deliver
Specialist
USS for head positionTransabdominal or transperineal USS to confirm OP vs OA position if clinical assessment uncertain
1
Prerequisites (must ALL be met)
- Full cervical dilatation
- Membranes ruptured
- Known presentation, position, and station
- Head ≤1/5 palpable abdominally
- Adequate analgesia (pudendal block, epidural, or spinal)
- Bladder emptied (catheterise)
- Informed consent obtained
2
Choice of instrument
- Ventouse (vacuum): cup applied to flexion point on fetal skull. Traction with maternal pushing
- Less maternal perineal trauma than forceps. Higher failure rate. Cannot use <34 weeks, face presentation, or after fetal scalp blood sampling
- Non-rotational forceps (Neville Barnes, Simpson's): for OA position, outlet deliveries
- Rotational forceps (Kielland's): for OP or OT positions — requires experienced operator
- Low-cavity outlet forceps (Wrigley's): for assisted delivery at CS (delivering head through uterine incision)
3
Procedure
- Perform in lithotomy position with adequate analgesia
- Consider mediolateral episiotomy (reduces OASIS risk)
- Apply instrument correctly, check no maternal tissue trapped
- Traction applied with contractions and maternal effort
- Abandon and proceed to CS if: no descent with first pull, 3 pulls without delivery (ventouse), or cup detaches 3 times
4
Trial of instrumental
- Performed in theatre ("trial in theatre") with everything prepared for immediate CS
- Indicated when: delivery not certain, mid-cavity, or 1/5 head palpable, OP position
- Clear plan: if instrumental fails → proceed to category 1 CS
Complications
- Maternal — perineal trauma: 3rd/4th degree tears (OASIS) more common with forceps. Mediolateral episiotomy reduces risk
- Maternal — vaginal/cervical lacerations: From instrument application
- Neonatal — cephalhaematoma: Subperiosteal bleeding (does not cross suture lines). More common with ventouse
- Neonatal — subgaleal haemorrhage: Bleeding beneath aponeurosis — crosses suture lines, can be life-threatening. More common with ventouse
- Neonatal — facial nerve palsy: From forceps blade pressure — usually temporary
- Failed instrumental: May require emergency CS — increased morbidity
UKMLA Exam Tips
- 1Prerequisites: fully dilated, membranes ruptured, ≤1/5 palpable abdominally, adequate analgesia, empty bladder
- 2Ventouse: less maternal trauma, higher failure rate. Cannot use <34 weeks
- 3Forceps: more maternal trauma (OASIS), lower failure rate. Can be used to rotate (Kielland's)
- 4Cephalhaematoma (does NOT cross suture lines) vs subgaleal haemorrhage (DOES cross suture lines — dangerous)
- 5Mediolateral episiotomy (not midline) is UK standard — reduces 3rd/4th degree tears
- 6Trial in theatre: instrumental attempted with immediate CS backup if it fails
practicetest your knowledge on instrumental deliveryApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — obstetrics and beyond.
open q-bank