Instrumental Delivery (Forceps and Ventouse)

1. Clinical Overview

Summary

Instrumental delivery (also termed Operative Vaginal Delivery [OVD] or Assisted Vaginal Delivery [AVD]) refers to the use of forceps or ventouse (vacuum extractor) to expedite vaginal birth during the second stage of labour when maternal effort alone is insufficient or contraindicated. This procedure is performed in approximately 10–15% of all vaginal deliveries in the United Kingdom, with significant variation internationally. [1,2]

The principal indications include presumed fetal compromise (non-reassuring cardiotocography [CTG]), prolonged second stage of labour (defined as > 3 hours in nulliparous women with regional anaesthesia, > 2 hours without; > 2 hours in multiparous women with regional anaesthesia, > 1 hour without), maternal exhaustion, and maternal medical conditions precluding prolonged Valsalva manoeuvres (e.g., cardiac disease, severe hypertension, proliferative retinopathy, intracranial pathology). [3,4]

Before attempting instrumental delivery, strict prerequisites must be fulfilled:

• Full cervical dilatation (10 cm)
• Vertex presentation (or after-coming head in breech)
• Head engaged (leading bony point at or below ischial spines; station 0 or lower)
• Known position of the fetal head (occiput anterior [OA], occiput transverse [OT], or occiput posterior [OP])
• Ruptured membranes
• Adequate analgesia (epidural, spinal, or pudendal block)
• Empty bladder (catheterisation)
• Informed consent
• Experienced operator with skills appropriate to the clinical scenario
• Preparations for immediate caesarean section if the procedure fails

The choice between forceps and ventouse depends on clinical circumstances (gestation, station, position, urgency), operator experience, and maternal preference. Forceps have higher success rates (~95%) but are associated with increased maternal perineal trauma, particularly third- and fourth-degree tears (obstetric anal sphincter injuries [OASI]). Ventouse has lower maternal trauma but higher rates of neonatal scalp injuries (cephalhaematoma, subgaleal haemorrhage) and a higher failure rate (~15%). [5,6]

Complications include maternal perineal and vaginal trauma, postpartum haemorrhage, and neonatal injuries (cephalhaematoma, facial nerve palsy, intracranial haemorrhage). Failed instrumental delivery necessitates immediate caesarean section; the use of sequential instruments (switching from ventouse to forceps) carries increased neonatal morbidity and should be undertaken only by experienced operators. [7,8]

Clinical Pearls

"Prerequisites Checklist": Before every instrumental delivery, systematically confirm: Fully dilated, Head engaged (≤0 station), Position known, Membranes ruptured, Adequate analgesia, Bladder empty, Informed consent, Theatre available.

"Forceps = Higher Success, Higher Maternal Trauma": Forceps achieve delivery in ~95% of cases but double the risk of third- and fourth-degree perineal tears compared to ventouse.

"Ventouse = Lower Maternal Trauma, Higher Neonatal Scalp Injury": Ventouse reduces severe perineal trauma but increases cephalhaematoma (incidence 10–15%) and carries risk of life-threatening subgaleal haemorrhage.

"Three Pulls Rule": If delivery is not imminent after traction during three consecutive contractions (or if ventouse cup detaches three times), abandon the procedure and proceed to caesarean section.

"Kielland's = Rotational Expert Only": Kielland's forceps for rotational delivery (OT/OP → OA) should only be performed by senior operators experienced in rotational techniques, ideally in theatre.

"Subgaleal Haemorrhage = Neonatal Emergency": Subgaleal haemorrhage (bleeding between galea aponeurotica and periosteum) can cause hypovolaemic shock and death. Monitor all ventouse-delivered infants for increasing head circumference, pallor, and shock.

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2. Epidemiology

Incidence and Trends

Demographics and Risk Factors

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3. Risk Factors for Requiring Instrumental Delivery

Understanding which women are at higher risk of requiring instrumental assistance allows anticipatory planning, optimised intrapartum care, and appropriate counselling.

Maternal Factors

Fetal and Obstetric Factors

Intrapartum Interventions

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4. Pathophysiology and Biomechanics

Normal Mechanism of Vaginal Delivery

Successful vaginal delivery requires coordinated interaction between:

1. Expulsive forces: Uterine contractions + maternal Valsalva effort
2. Fetal dimensions: Head size, moulding capacity, position (flexion vs deflexion)
3. Pelvic dimensions: Bony pelvis (inlet, mid-cavity, outlet) and soft tissue resistance

During the cardinal movements of labour, the fetal head undergoes:

• Engagement: Descent of the biparietal diameter through the pelvic inlet
• Descent: Progressive movement through the pelvis
• Flexion: Chin to chest (minimises presenting diameter)
• Internal rotation: OT or OP → OA alignment (to fit pelvic outlet)
• Extension: Head delivers under the pubic symphysis
• Restitution and external rotation: Head rotates to original position; shoulders deliver

Indications for Instrumental Assistance

Instrumental delivery is required when this mechanism fails due to:

Biomechanics of Forceps

Forceps are rigid metal instruments consisting of two blades designed to cradle the fetal head. They function by:

1. Application: Blades applied to the sides of the fetal head (biparietal, bimalar application).
2. Traction: Operator applies controlled traction along the pelvic curve (initially downward and backward, then upward as the head crowns).
3. Leverage: Forceps act as a Class 1 lever, with the fulcrum at the lock, transferring maternal effort (or operator traction) to the fetal head.
4. Rotation (Kielland's forceps): Kielland's forceps have minimal pelvic curve and a sliding lock, permitting rotation of the fetal head from OT or OP to OA before traction.

Advantages: High success rate (~95%); immediate traction possible; operator control over rate and force; can be used for after-coming head in breech.

Disadvantages: Higher risk of maternal perineal trauma (3rd/4th degree tears); requires adequate pelvic space; steeper learning curve.

Biomechanics of Ventouse (Vacuum Extraction)

Ventouse applies negative pressure (suction) to the fetal scalp via a cup (metal or silastic), creating an artificial caput (chignon) through which traction is applied. The cup is placed over the flexion point (3 cm anterior to the posterior fontanelle on the sagittal suture) to promote flexion and minimize presenting diameter.

Mechanism:

1. Suction: Negative pressure (typically 0.6–0.8 kg/cm² or 60–80 kPa) applied gradually or rapidly depending on cup type.
2. Chignon Formation: Scalp oedema forms under the cup, anchoring it to the fetal head.
3. Traction: Operator applies traction perpendicular to the cup, along the pelvic axis.
4. Rotation: Ventouse can facilitate autorotation (head rotates as it descends) but does not provide direct rotational control like Kielland's forceps.

Advantages: Lower maternal perineal trauma; easier application in mid-cavity; may be used with less pelvic space.

Disadvantages: Higher failure rate (~15%); increased neonatal scalp trauma (cephalhaematoma 10–15%, subgaleal haemorrhage 0.04%); cup detachment risk; slower than forceps in emergency situations.

Exam Detail: Subgaleal Haemorrhage Pathophysiology (High-Yield for MRCOG):

The subgaleal space (also called the subaponeurotic space) lies between the galea aponeurotica (epicranial aponeurosis) and the periosteum of the skull. This potential space:

• Extends from the orbital ridges anteriorly to the nuchal ridge posteriorly, and laterally to the temporal fascia.
• Can accommodate 260 mL of blood in a term neonate (approximately 80% of circulating blood volume).
• Contains emissary veins connecting to the dural sinuses.

Mechanism in Ventouse Delivery:

• Excessive traction or shear forces during vacuum extraction rupture emissary veins.
• Blood accumulates in the subgaleal space, dissecting across suture lines (unlike cephalhaematoma, which is limited by periosteal attachments and does not cross sutures).
• Rapid expansion causes hypovolaemic shock (tachycardia, pallor, hypotension, increasing head circumference).

Risk Factors: Prolonged vacuum application (> 20 minutes), multiple cup detachments, difficult extraction, cup placement away from flexion point, macrosomia.

Clinical Features: Boggy fluctuant swelling crossing suture lines; fluid thrill; increasing head circumference (serial measurements critical); signs of hypovolaemic shock develop over 6–72 hours.

Management: NICU admission, serial head circumference measurements, haematocrit monitoring, blood transfusion, coagulation screen (risk of consumptive coagulopathy).

Prognosis: Mortality 20–25% if untreated; survivors at risk of neurological sequelae.

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5. Indications

Instrumental delivery is indicated when expedited vaginal delivery is required and prerequisites are met. Indications are broadly categorised as fetal or maternal.

Fetal Indications

Maternal Indications

Exam Detail: MRCOG Viva: Definitions of Prolonged Second Stage

The second stage of labour begins with full cervical dilatation (10 cm) and ends with delivery of the baby.

It is traditionally divided into:

1. Passive second stage: Full dilatation confirmed, but no involuntary expulsive contractions or urge to push (woman may not be aware she is fully dilated). "Descent phase."
2. Active second stage: Expulsive contractions with pushing; or full dilatation with maternal effort (directed pushing); or descent of the presenting part visible.

Definitions of Prolonged Active Second Stage (NICE NG235, RCOG):

• Nulliparous with regional anaesthesia: > 3 hours
• Nulliparous without regional anaesthesia: > 2 hours
• Multiparous with regional anaesthesia: > 2 hours
• Multiparous without regional anaesthesia: > 1 hour

Passive second stage: Delay in passive second stage alone (without active pushing) is not an indication for intervention if progress is being made and fetal/maternal condition is reassuring. However, total duration of passive + active second stage should not exceed 4 hours (nulliparous) or 3 hours (multiparous) before intervention is considered.

Clinical Nuance: Intervention (oxytocin augmentation or instrumental delivery) may be appropriate before these time limits if there is:

• Concern about fetal wellbeing
• Lack of progressive descent
• Maternal request

Conversely, the second stage may safely continue beyond these limits if:

• Continuing descent is documented
• Maternal and fetal conditions are reassuring
• The woman wishes to continue

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6. Prerequisites for Instrumental Delivery

Before proceeding with instrumental delivery, all of the following prerequisites must be met. Failure to meet even one prerequisite is a contraindication.

Exam Detail: Station Classification and Clinical Implications (MRCOG High-Yield):

The station of the fetal head describes the position of the leading bony point (not caput or moulding) relative to the ischial spines.

ACOG/RCOG Classification:

• Outlet: Scalp visible at introitus without separating labia; fetal skull has reached pelvic floor; sagittal suture in AP diameter or ≤45° rotation; fetal head at/on perineum.
• Low: Leading point at +2 or lower, but not outlet. Subdivided: Low without rotation (≤45°) and Low with rotation (> 45°).
• Mid-Cavity: Head engaged (station 0 or below) but above +2.
• High: Head not engaged (above station 0). Contraindicated.

Clinical Tip: Always correlate VE station with abdominal palpation (fifths palpable). If 2/5 or more head palpable abdominally, head is not engaged and instrumental delivery is contraindicated.

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7. Classification of Instrumental Delivery

Instrumental deliveries are classified by station (height of head in pelvis) and rotation required. Classification predicts difficulty, complication rates, and success rates.

Classification by Station (ACOG/RCOG)

Classification by Rotation Required

Exam Detail: MRCOG Viva: Kielland's Forceps Technique

Kielland's forceps are specifically designed for rotational deliveries (OT or OP → OA). They differ from standard forceps in having:

1. Minimal pelvic curve: Allows rotation without locking against the pelvis.
2. Sliding lock: Permits asymmetric application if necessary (though symmetric application is preferred).
3. Knobs on handles: Indicate direction of the occiput (knobs point toward occiput).

Indications: OT or OP position requiring rotation to OA before traction.

Prerequisites (in addition to standard prerequisites):

• Experienced operator (consultant or senior trainee with Kielland's competency)
• Ideally performed as trial in theatre (high failure risk)
• Adequate analgesia (regional preferred)
• Exact position known (critical for safe rotation)

Technique (Simplified for Viva):

1. Assess position: Confirm OT or OP (identify posterior fontanelle, sagittal suture).
2. Select blade: Anterior blade (blade that will lie anteriorly after rotation) inserted first.
3. Application: Blades applied to biparietal diameter (sides of head). May use "wandering" technique (blade inserted posteriorly then rotated around head to anterior position).
4. Lock: Blades locked (check sagittal suture equidistant between blades; posterior fontanelle 1 finger-breadth above shanks).
5. Rotation: Gentle rotation of head from OT/OP to OA (rotate in direction of least resistance—usually shortest arc). Occiput rotates anteriorly.
6. Check position: Re-examine after rotation to confirm OA.
7. Traction: Apply traction as per standard forceps (downward and backward, then upward as head crowns).

Complications: Higher risk of maternal trauma (vaginal/cervical tears, especially if rotation forced against resistance); fetal trauma (skull fracture, intracranial haemorrhage if excessive force used).

Failure: If rotation cannot be achieved with gentle pressure, abandon and proceed to caesarean section.

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8. Instrument Selection: Forceps vs Ventouse

Instruments Available

Forceps Types

Ventouse (Vacuum Extractor) Types

Forceps vs Ventouse: Comparative Outcomes

Decision Algorithm: Forceps vs Ventouse

Choose FORCEPS when:

• Immediate delivery required (fetal compromise) — forceps faster and higher success rate
• Mid-cavity delivery with OP/OT position requiring rotation (Kielland's forceps)
• After-coming head in breech delivery
• Operator more experienced with forceps
• Previous failed ventouse (cup detachment ×3)

Choose VENTOUSE when:

• Maternal preference for lower perineal trauma
• Tight perineum or concern about OASI risk
• Low-cavity or outlet delivery (OA position)
• Less experienced operator (ventouse has shorter learning curve for non-rotational deliveries)
• OP position with expectation of autorotation (posterior metal cup)

Contraindications to VENTOUSE:

• Gestation less than 34 weeks (risk of intraventricular haemorrhage in preterm; fragile skull)
• Face or brow presentation
• Fetal bleeding disorder (haemophilia, von Willebrand disease, thrombocytopenia)
• Fetal bone demineralisation disorder (osteogenesis imperfecta)

Contraindications to FORCEPS:

• Inadequate pelvic space (absolute cephalopelvic disproportion)
• Unengaged head (station above 0)

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9. Procedure Technique

Pre-Procedure Preparation (Both Instruments)

1. Confirm Prerequisites: Systematically check all prerequisites (see Section 6).
2. Informed Consent: Explain indication, procedure, risks (perineal trauma, neonatal injury), benefits, and alternatives (awaiting spontaneous delivery, caesarean section). Document consent.
3. Assemble Team: Obstetrician (+ senior if required), midwife, anaesthetist (if in theatre or if epidural top-up needed), paediatrician/neonatal nurse.
4. Position: Lithotomy position; ensure adequate hip flexion and abduction; avoid excessive lithotomy angle (risk of nerve injury).
5. Ensure Adequate Analgesia: Top up epidural or perform spinal/pudendal block. Test sensation before proceeding.
6. Catheterise Bladder: Insert Foley catheter; empty bladder; leave catheter in situ or remove (operator preference).
7. Aseptic Technique: Perineal cleansing with antiseptic (chlorhexidine or povidone-iodine); sterile drapes.
8. Assess Position and Station: Careful vaginal examination:
   • Identify posterior fontanelle (triangular; three sutures meet forming "Y") and anterior fontanelle (diamond-shaped; four sutures meet).
   • Palpate sagittal suture (runs between fontanelles).
   • Determine position: OA (posterior fontanelle anterior, toward pubis), OP (posterior fontanelle posterior, toward sacrum), OT (posterior fontanelle transverse, toward side).
   • Assess station (leading bony point relative to ischial spines).
   • Assess moulding (overlap of skull bones: 0 = none, + = bones touching, ++ = overlapping but reducible, +++ = overlapping irreducible; severe moulding suggests CPD).
   • Assess caput (scalp oedema; does not indicate station).
9. Check Equipment:
   • Forceps: Check blades lock easily and symmetrically; blades should articulate without force.
   • Ventouse: Check vacuum pump functional; check cup integrity (no cracks); attach tubing; test vacuum.
10. Inform Theatre and Anaesthetic Team: Ensure theatre available and ready if procedure fails.

Forceps Delivery Technique

Standard Forceps (Non-Rotational: Neville Barnes, Simpson's)

1. Assemble Forceps: Check lock; ensure blades identified (left and right).
2. Insert Left Blade First:
   • Hold left blade in left hand.
   • Guide blade into vagina with right hand protecting maternal tissues.
   • Insert blade along left sidewall of pelvis, between fetal head and maternal pelvis.
   • Blade should lie along left side of fetal head (left ear/cheek).
   • Wandering technique: Insert blade posteriorly, then "wander" anteriorly around head, or insert directly to final position.
3. Insert Right Blade:
   • Hold right blade in right hand.
   • Guide with left hand.
   • Mirror image of left blade insertion (right sidewall, right side of head).
4. Lock Blades:
   • Bring handles together; they should lock easily with minimal force.
   • If lock is difficult, blades are incorrectly positioned (recheck and reapply).
5. Check Application (Critical):
   • Sagittal suture: Should be equidistant between the two blades (perpendicular to shanks). If not, application is asymmetric (risk of facial/skull trauma).
   • Posterior fontanelle: Should be 1–2 cm (one finger-breadth) above the shanks. If higher, head is deflexed (suboptimal). If at level of shanks or below, application may be on face (危险; reapply).
   • Fenestrations: Should admit one finger between blade and head (not too tight).
   • If application incorrect, remove blades and reapply.
6. Apply Traction:
   • Timing: Apply traction during uterine contractions. Maternal pushing assists (if able). Rest between contractions.
   • Direction: Initial traction downward and backward (following pelvic curve; toward floor). As head descends and crowns, traction becomes horizontal, then upward (toward ceiling) to deliver head under pubic symphysis by extension.
   • Force: Use steady, controlled traction. Avoid jerking or excessive force. If no descent after sustained traction during one contraction, reassess (position? asynclitism? CPD?).
   • Axis Traction: Some operators use Pajot's manoeuvre (one hand on handles applies traction; other hand on shanks directs force along pelvic axis).
7. Episiotomy:
   • Perform mediolateral episiotomy if perineum is tight or if blades cause excessive perineal stretch.
   • Timing: Usually as head distends perineum.
   • Technique: Scissors; cut from posterior fourchette at 45–60° angle (toward ischial tuberosity, away from anus).
8. Delivery of Head:
   • As head crowns, continue traction upward.
   • Deliver head slowly in a controlled manner (reduces perineal trauma).
9. Remove Blades:
   • Once head delivered, remove forceps blades (reverse order: right blade first, then left; or operator preference).
   • Do not apply traction to shoulders with forceps in place (risk of brachial plexus injury).
10. Complete Delivery:
    • Deliver anterior shoulder (downward traction on head), then posterior shoulder (upward traction).
    • Deliver body and clamp cord.
11. Inspect:
    • Examine baby for trauma (facial bruising, asymmetric crying [facial nerve palsy], cephalhaematoma, lacerations).
    • Examine perineum/vagina/cervix for trauma; repair as needed.

Rotational Forceps (Kielland's) – Overview

(Detailed Kielland's technique is beyond scope here; senior operator required. Key principles:)

1. Assess position: Confirm OT or OP.
2. Apply blades to biparietal diameter (may require "wandering" technique for anterior blade).
3. Check application: Sagittal suture equidistant; posterior fontanelle 1 finger above shanks; knobs point to occiput.
4. Rotate head: Gentle rotation from OT/OP to OA (90–180° arc). Rotate in arc of least resistance.
5. Recheck position: Confirm OA after rotation.
6. Apply traction: As per standard forceps.

Abandon if:

• Rotation cannot be achieved with gentle pressure (suggests CPD or bony obstruction).
• Maternal soft tissue trauma occurs during rotation.

Ventouse (Vacuum Extraction) Technique

1. Select Cup:
   • OA position, low-cavity: Soft cup or hand-held (Kiwi).
   • OP position or mid-cavity: Metal cup (larger posterior cup, e.g., Bird's posterior 6 cm).
2. Identify Flexion Point:
   • The flexion point (also called the median flexing point) is located 3 cm anterior to the posterior fontanelle, along the sagittal suture.
   • Placing the cup over the flexion point promotes flexion of the fetal head, minimising the presenting diameter (suboccipitobregmatic 9.5 cm).
   • Incorrect placement (too anterior or too posterior) → deflexion → larger diameter → failure.
3. Insert Cup:
   • Compress cup (if soft) or guide metal cup edge-on into vagina.
   • Place cup over flexion point on fetal scalp.
   • Check position: Centre of cup should be over flexion point; sagittal suture should run through centre of cup (or slightly off-centre toward occiput if using posterior cup for OP).
4. Check for Maternal Tissue:
   • Critical safety step: Sweep finger 360° around cup edge to ensure no maternal tissue (vaginal wall, cervix) trapped under cup.
   • Tissue entrapment → cervical/vaginal tears during traction.
5. Create Vacuum:
   • Stepwise: Gradually increase vacuum (0.2 kg/cm² increments every 2 minutes to 0.8 kg/cm² [80 kPa]). Allows chignon to form slowly; lower detachment risk.
   • Rapid: Increase vacuum directly to 0.8 kg/cm². Faster (useful if urgency); higher detachment risk.
   • Most operators use 0.6–0.8 kg/cm² (60–80 kPa) as standard.
6. Apply Traction:
   • Timing: With contractions; maternal pushing assists.
   • Direction: Pull perpendicular to the cup (not perpendicular to the floor; perpendicular to the cup surface), following the pelvic axis (initially downward and backward, then upward as head descends).
   • Checking descent: Between contractions, check that head is descending (station improving). If no descent after traction during two contractions, suspect malposition, asynclitism, or CPD.
7. Cup Detachment ("Pop-Off"):
   • If cup detaches, count the detachment.
   • Reapply cup over flexion point and recheck for trapped tissue.
   • Three detachments = abandon ventouse.
   • Cup detachment suggests:
     • Incorrect cup placement (not over flexion point)
     • Cephalopelvic disproportion
     • Excessive deflexion or asynclitism
     • Inadequate vacuum pressure
8. Duration Limit:
   • Maximum application time: 20 minutes from initial vacuum application to delivery.
   • Prolonged application increases scalp trauma (cephalhaematoma, subgaleal haemorrhage).
   • If delivery not achieved in 20 minutes, abandon.
9. Delivery of Head:
   • Continue traction until head crowns.
   • As head delivers, reduce vacuum and remove cup.
   • Deliver head slowly (controlled; reduces trauma).
10. Remove Cup:
    • Release vacuum; remove cup from scalp.
    • Complete delivery of shoulders and body.
11. Inspect:
    • Chignon: Scalp oedema/swelling under cup site (normal; resolves in 24–48 hours).
    • Cephalhaematoma: Firm, fluctuant swelling confined to one skull bone (does not cross suture lines); subperiosteal haemorrhage. Monitor; usually benign; resolves over weeks; may cause jaundice.
    • Subgaleal haemorrhage: Boggy, fluctuant swelling that crosses suture lines; increases over hours; may cause shock. Neonatal emergency—inform paediatrician immediately; NICU admission; serial head circumference measurements; monitor for anaemia/shock.
    • Scalp lacerations/abrasions: Common with metal cups; usually minor.
    • Examine perineum for trauma (less common than forceps, but still possible).

Failure Criteria (Both Instruments)

Abandon instrumental delivery and proceed to caesarean section if:

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10. Failed Instrumental Delivery

Failed instrumental delivery is defined as the inability to achieve vaginal delivery using the selected instrument despite correct technique and adequate effort. It occurs in approximately 5–10% of attempted instrumental deliveries (higher for ventouse ~10–15%, lower for forceps ~5%). [7,8]

Risk Factors for Failure

Management of Failed Instrumental Delivery

1. Abandon Early: If no progress after 3 pulls/contractions, or cup detaches ×3, do NOT persist. Continued attempts increase trauma without improving outcome.

2. Call for Senior Help: If not already present, call consultant obstetrician.

3. Consider Sequential Instrument Use (Controversial):

   • Sequential instruments: Switching from one instrument to another (typically ventouse → forceps).
   • Evidence: Cochrane review shows sequential instruments achieve vaginal delivery in ~60–70% of failed first-attempt cases, but are associated with increased neonatal trauma (cephalhaematoma, intracranial haemorrhage, low Apgar scores). [26]
   • Indications: May be considered if:
     • Senior experienced operator present
     • Head has descended significantly with first instrument (now at lower station)
     • Fetal condition allows time for second attempt
     • Woman strongly wishes to avoid caesarean (informed consent regarding increased neonatal risk)
   • Contraindications:
     • Fetal compromise (Category 1 urgency) — proceed to immediate caesarean
     • Significant maternal trauma from first attempt
     • Inexperienced operator
     • No descent with first instrument (suggests CPD)

4. Proceed to Emergency Caesarean Section:

   • Failed instrumental delivery is classified as Category 1 or Category 2 caesarean (depending on fetal condition).
   • Challenges:
     • Head may be deeply impacted in pelvis → difficult to disengage.
     • Use reverse breech extraction (push head up per vaginam while assistant delivers via caesarean) or use of Fetal Pillow (inflatable device inserted vaginally to elevate head).
   • Anaesthesia: Usually requires general anaesthesia (faster than spinal if Category 1; regional may be adequate if Category 2).

5. Debrief and Support:

   • Failed instrumental delivery is distressing for the woman and partner.
   • Provide postnatal debrief (explain what happened, why instrumental delivery failed, management plan).
   • Discuss implications for future pregnancies (not a contraindication to vaginal birth; success of instrumental delivery in subsequent pregnancy ~70%). [27]

Exam Detail: MRCOG Viva: Trial of Instrumental Delivery in Theatre

A trial of instrumental delivery (also called "trial of operative vaginal delivery in theatre") refers to an attempted instrumental delivery performed in the operating theatre, with the patient prepared for immediate caesarean section if the attempt fails.

Indications (Any ONE of the following suggests high failure risk → trial in theatre):

• Mid-cavity delivery (station 0 or +1)
• Rotational delivery (especially OP → OA)
• Suspected CPD (macrosomia, excessive moulding, small pelvis)
• Trainee operator (supervised by senior)
• Clinical uncertainty about feasibility of vaginal delivery

Procedure:

1. Consent: Explain to woman that caesarean section is likely if instrumental delivery fails; consent for both instrumental delivery and caesarean section.
2. Anaesthesia: Regional anaesthesia (spinal or epidural) already in place (can proceed to caesarean without delay). Ensure T4 sensory level (adequate for caesarean if required).
3. Preparation: Woman positioned in lithotomy; abdomen prepped and draped for caesarean; surgical team scrubbed; theatre ready.
4. Attempt Instrumental Delivery: Operator attempts delivery using forceps or ventouse (usual technique).
5. Outcome:
   • Success: Vaginal delivery achieved → complete delivery; no laparotomy required.
   • Failure: Delivery not progressing after 3 pulls or other failure criteria → proceed immediately to caesarean section (team already prepared; minimal delay).

Advantages:

• No delay if instrumental delivery fails (theatre and anaesthesia already in place)
• Safer for woman and baby (avoids prolonged failed attempts in delivery room, then transfer to theatre with worsening fetal compromise)
• Allows attempt at vaginal delivery in borderline cases (rather than proceeding directly to caesarean)

Note: Trial of instrumental delivery does not mean "prolonged attempts are acceptable." The same failure criteria apply (3 pulls; no descent; cup detachment ×3; 20-minute limit). The difference is the setting (theatre vs delivery room), not the technique or persistence.

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11. Complications

Maternal Complications

Neonatal Complications

Exam Detail: MRCOG Viva: How to Diagnose and Distinguish Cephalhaematoma vs Subgaleal Haemorrhage

Examination Tip: In an OSCE or viva, if presented with a neonate after ventouse delivery with scalp swelling:

1. Ask: "Does the swelling cross suture lines?" (No = cephalhaematoma; Yes = subgaleal haemorrhage)
2. Assess: Vital signs (shock?), serial head circumference (increasing?), colour (pale?).
3. Examine: Palpate swelling (firm/fluctuant = cephalhaematoma; boggy/fluid thrill = subgaleal).
4. Act: Cephalhaematoma → reassure, observe. Subgaleal → NICU, transfuse, serial measurements.

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12. Outcomes and Prognosis

Maternal Outcomes

Neonatal Outcomes

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13. Prevention Strategies

Preventing the Need for Instrumental Delivery

Preventing Complications of Instrumental Delivery

Reducing Maternal Trauma (OASI Care Bundle)

The RCOG OASI Care Bundle reduces third- and fourth-degree tears by ~20–30%: [29]

1. Manual perineal protection during delivery of head (Hands-on technique: support perineum with one hand; control delivery of head with other).
2. Slow, controlled delivery of head (avoid rapid expulsion).
3. Mediolateral episiotomy (45–60° angle) when indicated (tight perineum, instrumental delivery, impending severe tear).
4. Lithotomy positioning with care (avoid excessive hip flexion/abduction → nerve injury).

Reducing Neonatal Scalp Trauma

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14. Guidelines and Evidence

Key Guidelines

Key Evidence

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15. Examination Focus (MRCOG)

High-Yield Viva Topics

1. Prerequisites for Instrumental Delivery

   Question: "What must be confirmed before attempting instrumental delivery?"

   Model Answer:

   • Fully dilated cervix (10 cm)
   • Head engaged (station ≤0; leading bony point at or below ischial spines)
   • Vertex presentation (or after-coming head in breech)
   • Position known (OA, OT, OP; identify posterior fontanelle and sagittal suture)
   • Ruptured membranes (ARM if intact)
   • Adequate analgesia (epidural, spinal, or pudendal block)
   • Empty bladder (catheterise)
   • Informed consent (verbal; written if time permits)
   • Experienced operator (appropriate to difficulty)
   • Theatre available (for immediate caesarean if fails)
   • Neonatal resuscitation available (paediatrician or ANNP)

2. Classification by Station

   Question: "Define outlet, low, mid-cavity, and high instrumental delivery."

   Model Answer:

   • Outlet: Scalp visible at introitus; head on pelvic floor; station +2 to +3; sagittal suture AP or ≤45° rotation.
   • Low: Leading point +2 or below, but not outlet. Subdivided: low without rotation (≤45°) and low with rotation (> 45°).
   • Mid-cavity: Head engaged (station 0 or +1) but above +2.
   • High: Head not engaged (above station 0). Contraindicated for instrumental delivery.

3. Forceps vs Ventouse: Comparative Outcomes

   Question: "Compare forceps and ventouse in terms of maternal and neonatal outcomes."

   Model Answer:

   • Success rate: Forceps higher (~95%) vs ventouse (~85%).
   • Maternal perineal trauma (OASI): Forceps higher (10–13%) vs ventouse (5–7%).
   • Neonatal cephalhaematoma: Ventouse higher (10–15%) vs forceps (2–5%).
   • Subgaleal haemorrhage: Ventouse higher (0.04–0.06%) vs forceps (rare).
   • Facial nerve palsy: Forceps higher (~1%) vs ventouse (rare).
   • Overall serious neonatal morbidity: No significant difference.

   Conclusion: Choice depends on clinical scenario, operator experience, maternal preference. Forceps for immediate delivery (fetal compromise), ventouse for lower maternal trauma risk.

4. Failed Instrumental Delivery

   Question: "What are the criteria for abandoning instrumental delivery, and what should you do next?"

   Model Answer: Abandon if:

   • No descent after traction during 3 consecutive contractions
   • Ventouse cup detaches 3 times
   • Duration > 20 minutes (ventouse) or > 3 pulls (forceps)
   • Maternal or fetal trauma
   • Operator uncertainty

   Management:

   • Call senior help (if not present)
   • Consider sequential instruments (ventouse → forceps) only if: Senior operator, head has descended significantly, fetal condition allows, informed consent (but warn of increased neonatal morbidity)
   • Proceed to emergency caesarean (Category 1 or 2 depending on urgency)
   • Be prepared for impacted head (reverse breech extraction, fetal pillow)
   • Debrief woman postnatally

5. Subgaleal Haemorrhage

   Question: "A baby is born by ventouse. 12 hours later, the midwife calls you because the baby's head circumference has increased from 35 cm to 38 cm. What is your differential diagnosis and management?"

   Model Answer: Diagnosis: Subgaleal haemorrhage (most likely).

   • Bleeding between galea aponeurotica and periosteum; crosses suture lines.
   • Can hold 260 mL blood (80% of neonatal circulating volume).
   • Causes hypovolaemic shock.

   Clinical features: Increasing head circumference; boggy fluctuant swelling crossing sutures; pallor; tachycardia; hypotension; shock.

   Differential: Cephalhaematoma (does NOT cross sutures; does NOT increase head circumference rapidly; no shock).

   Management:

   • Urgent assessment (ABC; examine baby; palpate swelling)
   • NICU admission
   • Serial head circumference (hourly initially)
   • Monitor vital signs and capillary refill
   • Blood tests: FBC (haematocrit), coagulation screen
   • Blood transfusion (crossmatch urgently; may need 40–80 mL/kg)
   • FFP and platelets if coagulopathy
   • Avoid phototherapy initially (increases cerebral blood flow)
   • Inform senior neonatologist and obstetrician

   Prognosis: Mortality 20–25% if untreated; good outcome if recognised early and transfused.

6. Kielland's Forceps

   Question: "When would you use Kielland's forceps, and what are the key technical differences from standard forceps?"

   Model Answer: Indications: Rotational delivery (OT or OP → OA).

   Design Differences:

   • Minimal pelvic curve (allows rotation without locking against pelvis)
   • Sliding lock (permits asymmetric application if needed)
   • Knobs on handles (point toward occiput)

   Prerequisites (in addition to standard):

   • Senior/experienced operator (consultant or senior trainee with Kielland's competency)
   • Ideally trial in theatre (high failure risk)
   • Exact position known (critical for safe rotation)

   Key Steps:

   • Apply blades to biparietal diameter (may use "wandering" technique for anterior blade)
   • Check application (sagittal suture equidistant; posterior fontanelle 1 finger above shanks)
   • Rotate head from OT/OP to OA (gentle pressure; rotate in arc of least resistance)
   • Recheck position (confirm OA)
   • Apply traction

   Abandon if: Rotation not achievable with gentle pressure (suggests CPD or bony obstruction).

7. OASI Prevention (Care Bundle)

   Question: "What measures can reduce the risk of third- and fourth-degree tears during instrumental delivery?"

   Model Answer: RCOG OASI Care Bundle (reduces OASI by 20–30%):

   1. Manual perineal protection (hands-on: support perineum; control head delivery)
   2. Slow, controlled delivery of head (avoid rapid expulsion)
   3. Mediolateral episiotomy (45–60° angle) when indicated (tight perineum, instrumental delivery, impending severe tear)
   4. Communication with woman (stop pushing as head crowns; pant)

   Additional:

   • Avoid midline episiotomy (increases OASI risk)
   • Adequate analgesia (allows controlled delivery)
   • Experienced operator

8. Trial of Instrumental Delivery in Theatre

   Question: "What is a trial of instrumental delivery, and when is it indicated?"

   Model Answer: Definition: Attempted instrumental delivery performed in operating theatre, with patient prepared for immediate caesarean section if attempt fails.

   Indications (high failure risk):

   • Mid-cavity delivery (station 0 or +1)
   • Rotational delivery (OP or OT)
   • Suspected CPD (macrosomia, moulding, small pelvis)
   • Trainee operator (supervised)
   • Clinical uncertainty about feasibility

   Procedure:

   • Consent for both instrumental and caesarean
   • Regional anaesthesia already in place (T4 level for caesarean)
   • Patient positioned; abdomen prepped and draped; surgical team scrubbed
   • Attempt delivery (same technique and failure criteria as delivery room)
   • If successful → complete vaginal delivery; if fails → immediate caesarean (no delay; theatre ready)

   Advantage: Minimises delay if instrumental delivery fails; safer than prolonged attempts in delivery room.

OSCE Scenarios

1. Consent for Instrumental Delivery

   Scenario: "A nulliparous woman has been pushing for 3 hours with an epidural. CTG is reassuring. Fetal head is OA, station +1. You plan forceps delivery. Obtain consent."

   Key Points:

   • Introduce self; confirm identity
   • Explain situation: "You've been pushing for 3 hours. Baby's head is low but hasn't quite delivered. Baby is doing well on the monitor, so we have time to discuss options."
   • Explain indication: Prolonged second stage (> 3 hours with epidural).
   • Explain options: 1) Continue pushing (but unlikely to deliver without help), 2) Instrumental delivery (forceps or ventouse), 3) Caesarean section.
   • Recommend instrumental delivery (forceps): "I recommend we help baby out using forceps—metal instruments that fit around baby's head to guide baby out while you push."
   • Explain procedure: "I'll examine you to check baby's position, then place the forceps and gently pull while you push with contractions."
   • Risks (maternal): "There's a risk of tearing (around 10–15% chance of significant tear that needs repair in theatre with anaesthetic). You'll likely need a cut (episiotomy) to make space. There may be bruising and pain afterward."
   • Risks (neonatal): "Baby may have some bruising or swelling on the head (usually minor and goes away). There's a small risk of nerve injury to the face, but this usually recovers."
   • Benefits: "Much more likely to achieve vaginal delivery compared to continuing to push. Faster than caesarean."
   • Alternative: "If forceps don't work, we'd need to do a caesarean section. We're prepared for that—the operating theatre is ready."
   • Check understanding; allow questions; obtain verbal consent (document).

2. Managing Failed Ventouse

   Scenario: "You are the registrar performing a ventouse delivery for prolonged second stage. The cup has detached twice. On the third pull, the cup detaches again. What do you do?"

   Key Actions:

   • Recognise failure criterion: Cup detachment ×3 → abandon ventouse.
   • Stop procedure immediately.
   • Call for senior help (consultant obstetrician).
   • Reassess: VE (position? station? descent achieved?).
   • Discuss with consultant: Options are 1) Sequential instruments (forceps), 2) Caesarean section.
   • If senior suggests forceps trial: Ensure woman consents; explain increased neonatal risk with sequential instruments; ensure theatre ready; senior to perform (or supervise).
   • If senior recommends caesarean (or if no descent with ventouse): "The vacuum cup has come off three times, which means we can't safely continue. We need to deliver your baby by caesarean section to keep both of you safe. The operating theatre is ready; we'll get you there right away."
   • Document clearly: Indication for instrumental delivery, attempts made, reason for failure, decision-making, consent for caesarean.
   • Debrief woman postnatally (explain what happened, why ventouse failed, that it's not her fault).

3. Recognising and Managing Subgaleal Haemorrhage

   Scenario: "You are the paediatric SHO called to see a 24-hour-old baby born by ventouse. The midwife is concerned about increasing head size. On examination, the baby is pale, tachycardic (HR 180), and has a large boggy swelling on the scalp that crosses the suture lines. What is your diagnosis and management?"

   Diagnosis: Subgaleal haemorrhage (life-threatening emergency).

   Immediate Actions:

   • A, B, C assessment
   • Call for senior help (senior paediatrician/neonatologist)
   • Measure head circumference (compare to birth measurement; serial measurements hourly)
   • IV access (or IO if difficult)
   • Bloods: FBC (Hb/Hct urgent), Group & Save (crossmatch), coagulation screen
   • Monitor vital signs continuously (HR, BP, RR, sats, capillary refill, temperature)
   • Fluid resuscitation: 10–20 mL/kg 0.9% saline bolus if shocked
   • Prepare for blood transfusion: Crossmatch 40–80 mL/kg PRBC (baby may need near-total blood volume replacement)
   • FFP and platelets if coagulopathy (DIC risk)
   • Transfer to NICU immediately
   • Avoid phototherapy initially (increases cerebral blood flow; may worsen bleeding)
   • Inform obstetric team (documentation; debrief mother)
   • Reassess frequently: Serial head circumference, Hct, vital signs
   • Transfuse early: Do not wait for profound shock; subgaleal space holds 260 mL (80% of blood volume).

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16. Patient and Layperson Explanation

What is an Instrumental Delivery?

Sometimes during labour, your baby needs help to be born. When this happens, your doctor or midwife can use special instruments to gently guide your baby out while you push. There are two types of instruments:

1. Forceps: Metal tongs shaped like large spoons that fit carefully around your baby's head.
2. Ventouse (Vacuum Extractor): A soft or firm cup placed on your baby's head with gentle suction to help guide the baby out.

Why Might I Need an Instrumental Delivery?

You may need help if:

• You've been pushing for a long time and are very tired.
• Your baby's heartbeat shows signs of stress and needs to be born soon.
• You have a medical condition (like heart or blood pressure problems) that means prolonged pushing isn't safe for you.
• Your baby is in a tricky position and needs a little help to turn or come out.

How is it Done?

• You'll be positioned comfortably (usually with your legs supported).
• We'll make sure you have good pain relief (usually an epidural or injection to numb the area).
• Your doctor will examine you to check your baby's position.
• The forceps or ventouse cup is carefully placed, and gentle pulling is applied while you push with your contractions.
• In most cases, your baby is born within a few minutes.

Is it Safe?

Yes, instrumental delivery is very safe and has been used for many years. However, like all medical procedures, there are some risks:

For you:

• Tearing: You may have a tear that needs stitches (around 1 in 10 women have a more significant tear involving the muscle near the back passage). We try to prevent this with careful technique and sometimes a small cut (episiotomy).
• Bruising and soreness: The area may be sore for a few weeks, but pain relief and gentle care help it heal.

For your baby:

• Bruising or swelling: Your baby may have a mark or swelling where the instrument was placed. This usually goes away within a few days or weeks.
• Rarely, more serious problems: Very occasionally, babies can have injuries like bleeding under the scalp. We watch all babies carefully after instrumental delivery.

What Happens if it Doesn't Work?

If the instrumental delivery doesn't work after a few careful attempts, we'll deliver your baby by caesarean section (an operation). We always have a plan in place and a theatre ready just in case.

Will I Need an Instrumental Delivery Again?

Not necessarily. Most women who have an instrumental delivery with their first baby go on to have a normal delivery with their next baby. Every labour is different.

Can I Ask Questions?

Absolutely. Please ask your midwife or doctor any questions you have. We want you to feel informed and supported.

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Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances and local protocols. Always consult senior colleagues and appropriate specialists when managing complex cases. This topic has been prepared for postgraduate medical examination (MRCOG) candidates and practising obstetricians.