Instrumental Delivery
Instrumental delivery uses forceps or vacuum (ventouse) to assist vaginal delivery in the second stage of labour when there is delay, fetal compromise, or maternal indication.
Key Facts
Instrumental delivery rate in the UK: approximately 12-15% of all deliveries Ventouse (vacuum) and forceps are the two methods; choice depends on clinical situation and operator experience Prerequisites (FORCEPS mnemonic): Full dilatation, OA/OP position known, Ruptured membranes, Catheter in situ, Epidural/analgesia, Presenting part at or below spines, Sphincter (bladder) empty, Sagittal suture position identified Ventouse is associated with more failures but fewer maternal injuries than forceps Forceps have higher success rate but increased risk of perineal trauma (3rd/4th degree tears) Maximum 3 pulls with ventouse and 3 cup detachments before abandoning (RCOG GTG 26) Kielland's forceps for rotational delivery; Neville Barnes/Simpson's for non-rotational All instrumental deliveries should have a paired cord blood gas taken
Overview
Key Facts
Instrumental delivery refers to the use of forceps or vacuum extractor to assist vaginal delivery during the second stage of labour. It is a core obstetric skill required when spontaneous delivery is not progressing or when expedited delivery is needed.
Epidemiology
- Instrumental delivery rate in the UK: 12-15% of all births
- Ventouse accounts for approximately 60% and forceps 40% of instrumental deliveries
- Higher rates in nulliparous women, epidural use, and occipitoposterior position
- Declining slightly with increasing caesarean section rates
Aetiology (Indications)
- Prolonged second stage: nulliparous >2 hours active pushing, multiparous >1 hour
- Fetal compromise: pathological CTG in second stage
- Maternal exhaustion
- Maternal medical conditions: avoid Valsalva (cardiac disease, intracranial pathology, hypertensive crisis)
- Aftercoming head of breech (forceps only)
Pathophysiology
- Ventouse creates a chignon (artificial caput) on the fetal scalp; traction assists descent and delivery
- Forceps cradle the fetal head; traction and (if rotational) rotation aid delivery
- Force is applied along the pelvic curve to follow the axis of the birth canal
Clinical Presentation
Assessment Before Instrumental Delivery
- Confirm full dilatation
- Assess fetal position (OA, OP, OT - clinical and/or ultrasound)
- Station: at or below ischial spines
- Adequate contractions
- Adequate analgesia (pudendal block for ventouse, regional/spinal for mid-cavity/rotational)
- Empty bladder (catheterise)
- Informed consent
Classification of Instrumental Delivery
- Outlet: fetal scalp visible, minimal rotation needed
- Low-cavity: station at +2cm or more, ≤45° rotation
- Mid-cavity: station above +2cm but head engaged, may need >45° rotation
Red Flags
- Head not engaged (above ischial spines) - contraindication
- Unknown fetal position
- Prematurity (<34 weeks for ventouse due to risk of subgaleal haemorrhage)
- Suspected fetal bleeding disorder
- Failure to deliver with 3 pulls or 3 cup detachments
Differential Diagnosis
| Diagnosis | Key Features | Investigation |
|---|---|---|
| Normal second stage | Progressing, no indication for intervention | Partogram review |
| Obstructed labour | No descent despite good contractions, caput/moulding | Vaginal examination |
| Cephalopelvic disproportion | Head not engaging, significant moulding | Clinical assessment |
| Malpresentation | Brow/face presentation | Vaginal examination, USS |
| Fetal compromise | Pathological CTG, meconium | CTG, fetal blood sampling |
Diagnosis / Investigation
Bedside
- Abdominal palpation (fifths palpable - must be 0/5 or 1/5)
- Vaginal examination (position, station, moulding, caput, dilatation)
- CTG assessment
- Ultrasound for fetal position if uncertain
- Catheterise bladder
Bloods
- Group and save (should already be available)
- Paired cord blood gases after delivery (arterial and venous)
Imaging
- Intrapartum ultrasound increasingly used to confirm fetal position before instrumental delivery
Special Tests
- Fetal blood sampling may have been performed if CTG concerns preceded decision for instrumental delivery
Management
Non-pharmacological
- Informed consent (including discussion of risks, alternative of CS)
- Appropriate birth setting (theatre for mid-cavity or rotational, may be room for outlet)
- Neonatal team present or on standby
- Paediatrician present for all mid-cavity and rotational deliveries
Pharmacological
- Analgesia: pudendal block + perineal infiltration (outlet ventouse), spinal/epidural (mid-cavity/rotational forceps)
- Oxytocin: may be started/continued for uterine contractions
- Active management of third stage: oxytocin 10 IU IM
Surgical/Interventional
- Ventouse (vacuum): Kiwi cup, metal cup (Malmström), or silicone cup applied to flexion point
- Forceps: Neville Barnes or Simpson's (non-rotational), Kielland's (rotational), Wrigley's (outlet/at CS)
- Episiotomy: mediolateral episiotomy recommended for forceps delivery
- Sequential instrumentation: ventouse followed by forceps is associated with increased neonatal morbidity - should only be performed by senior obstetrician
- Trial of instrumental in theatre: mid-cavity or uncertain deliveries with immediate access to CS if unsuccessful
Referral Criteria
- Failed instrumental delivery: immediate caesarean section
- Third/fourth degree tear: repaired by experienced operator in theatre
- Neonatal assessment after all instrumental deliveries
- Follow-up at 6-12 weeks for perineal clinic if significant tear
Prognosis
- Overall success rate: ventouse 80-85%, forceps 90-95%
- 3rd/4th degree perineal tear: 8-12% with forceps, 4-6% with ventouse
- Neonatal cephalhaematoma: 6-12% with ventouse
- Neonatal subgaleal haemorrhage: 0.6% with ventouse (potentially life-threatening)
- Neonatal facial nerve palsy: 0.5-1% with forceps (usually temporary)
- Maternal urinary incontinence: increased risk with forceps
- Subsequent delivery: 70-80% achieve spontaneous vaginal delivery
Other Relevant Information
Ventouse vs Forceps Comparison
| Feature | Ventouse | Forceps |
|---|---|---|
| Success rate | 80-85% | 90-95% |
| Maternal perineal trauma | Lower | Higher |
| Cephalhaematoma | Higher | Lower |
| Subgaleal haemorrhage | Higher (rare) | Minimal |
| Facial nerve injury | No | Possible |
| Retinal haemorrhage | More common | Less common |
| Analgesia requirement | Pudendal block may suffice | Regional/spinal preferred |
RCOG Classification of Instrumental Delivery
| Type | Station | Rotation |
|---|---|---|
| Outlet | Scalp visible | ≤45° |
| Low | At +2cm or below | ≤45° |
| Mid-cavity | Above +2cm but engaged | May be >45° |