Operative Obstetrics — Forceps & Vacuum

Operative vaginal delivery (OVD) is the use of forceps or a vacuum (ventouse) to assist completion of the second stage of labour. It is a high-yield "prerequisites and classification" topic: NEET PG reliably tests the mandatory conditions, the ACOG/station-based classification, the forceps-vs-vacuum contrast, contraindications, and the signature complications (subgaleal haematoma, cephalhaematoma). Master the lists and cut-offs — that is where the marks are.

Definition & overview

Operative vaginal delivery is delivery of the foetus through the vagina with the aid of a mechanical instrument applied to the foetal head when spontaneous delivery is not imminent or is unsafe. The two instruments are:

• Obstetric forceps — paired metal blades that grasp the foetal head; provide traction ± rotation, and a protective "cage" for the head.
• Vacuum extractor (ventouse) — a cup (metal/silastic/soft) applied to the foetal scalp connected to a vacuum pump; works by traction only with the principle that the flexion point keeps the head flexed.

OVD now accounts for a falling proportion of deliveries (rising caesarean rates), but remains essential to avoid prolonged second stage and the maternal/foetal risks of an emergency caesarean at full dilatation.

High-yield: Forceps = traction and rotation possible; Vacuum = traction only (auto-rotation may occur passively, but you do not actively rotate with a ventouse).

Components of forceps

A standard obstetric forceps (e.g., Wrigley's for outlet, Simpson's/Das, Kielland's for rotation) has:

• Blade — with two curves: the cephalic curve (fits the foetal head) and the pelvic curve (fits the maternal sacral hollow). Kielland's forceps have a minimal/absent pelvic curve plus a sliding lock — designed for rotation of the head in the mid-pelvis (e.g., deep transverse arrest, occipito-posterior).
• Shank, lock (English lock most common), and handle.

Forceps	Main use	Distinguishing feature
Wrigley's	Outlet / lift-out, caesarean head delivery	Short, light
Simpson's / Das	Low & outlet traction	Fenestrated blades, pronounced curves
Kielland's	Rotation (deep transverse arrest, OP)	Sliding lock, no/minimal pelvic curve
Piper's	Aftercoming head of breech	Long shank, reverse pelvic curve

High-yield: Piper's forceps = aftercoming head of breech. Kielland's = rotational forceps for deep transverse arrest.

Prerequisites for operative vaginal delivery

These are the most examined facts. A widely used mnemonic is "ABCDEFGHIJ" but the practical checklist is best learned as the conditions that must all be satisfied before applying any instrument.

Mnemonic — the head must be ready (think "Fully dilated, Engaged, Empty bladder"):

1. Cervix fully dilated (10 cm) and membranes ruptured.
2. Head engaged — vertex at or below the ischial spines (station 0 or lower); no more than 1/5 palpable abdominally.
3. Presentation known and suitable — vertex (or face mento-anterior for forceps); position precisely determined.
4. Adequate pelvis — no cephalopelvic disproportion (CPD).
5. Bladder empty (catheterise).
6. Adequate analgesia/anaesthesia (pudendal/epidural).
7. Consent obtained, experienced operator, and back-up plan (theatre ready for caesarean if failure).
8. Estimated foetal weight considered; no contraindication (e.g., bleeding disorder for vacuum).

High-yield: The head must be engaged and the cervix fully dilated — these are absolute. A non-engaged head or incompletely dilated cervix is an absolute contraindication to OVD.

High-yield: Empty the bladder before any instrumental delivery — a full bladder obstructs descent and risks bladder injury.

Classification (ACOG / station-based)

Classification is by station of the leading bony point and degree of rotation. This is a favourite MCQ. Station is measured relative to the maternal ischial spines (0 = at spines; +1 to +5 below).

Type	Station	Rotation
Outlet	Scalp visible at introitus without separating labia; skull on pelvic floor; sagittal suture in AP diameter or ≤ 45°	≤ 45°
Low	Leading point at ≥ +2 station, not on pelvic floor	Subdivided: ≤45° vs >45°
Mid	Head engaged, leading point above +2 (between 0 and +2)	Any
High	Head not engaged (above the spines)	—

High-yield: High forceps/vacuum (unengaged head) is obsolete and contraindicated — caesarean is the answer. Outlet and low procedures carry the lowest morbidity.

Stepwise approach (the "flow"): Confirm prerequisites → catheterise bladder → confirm position & station → apply instrument correctly (forceps blades along cephalic curve / vacuum cup over flexion point) → check application (no maternal tissue trapped; cup centred over sagittal suture ~3 cm anterior to posterior fontanelle) → traction synchronised with uterine contractions and maternal effort → deliver head → controlled delivery of body → inspect for genital tract trauma.

Vacuum (ventouse): principles & technique

• Flexion (median) point = on the sagittal suture, about 3 cm in front of the posterior fontanelle (i.e., ~6 cm from anterior fontanelle). Centring the cup here maintains flexion and presents the smallest diameter.
• Vacuum pressure built to ~0.6–0.8 kg/cm² (≈ 500–600 mmHg).
• An artificial swelling under the cup, the chignon, forms — this is expected and resolves.
• Traction during contractions, perpendicular to the cup.

Rules to abandon (vacuum failure):

• No descent after 3 pulls, OR
• 3 cup detachments ("pop-offs"), OR
• delivery not achieved within ~15–20 minutes, OR cup repeatedly slips.

High-yield: Avoid sequential use of instruments (vacuum then forceps) where possible — it markedly increases neonatal trauma. If the first instrument fails, reassess for caesarean rather than reflexively switching.

Forceps vs Vacuum — the core comparison table

Feature	Forceps	Vacuum (Ventouse)
Mechanism	Traction + rotation	Traction only
Maternal analgesia needed	More (regional/pudendal)	Less
Maternal trauma (3rd/4th-degree tears)	Higher	Lower
Foetal/neonatal trauma	Facial nerve palsy, facial marks, skull #	Cephalhaematoma, subgaleal haemorrhage, retinal haemorrhage
Failure rate	Lower	Higher
Can be used <34 weeks (preterm)	Yes	No (avoid — fragile skull/scalp)
Speed	Faster	Slower
Operator skill	Higher	Easier to learn
Cephalhaematoma	Less	More common

High-yield: Vacuum is contraindicated in prematurity (<34 weeks), face/brow presentation, and suspected fetal coagulopathy/thrombocytopenia. Use forceps instead in these settings (or caesarean).

High-yield: Compared head-to-head: vacuum → more cephalhaematoma & retinal haemorrhage but less maternal trauma; forceps → more maternal perineal trauma and facial injury/nerve palsy.

Indications

Maternal/foetal/labour indications (think "to shorten or avoid maternal pushing, or expedite for foetal compromise"):

• Foetal: suspected foetal compromise / non-reassuring CTG in second stage.
• Maternal: to avoid Valsalva — cardiac disease (e.g., severe valve lesions), severe hypertension/eclampsia risk, intracranial pathology (aneurysm), severe respiratory disease, myasthenia, spinal cord injury.
• Labour: prolonged/inadequate progress in second stage (the most common indication), maternal exhaustion.
• Aftercoming head of breech (forceps — Piper's).

Contraindications

Absolute:

• Unengaged head / station above spines (high station).
• Cervix not fully dilated.
• Cephalopelvic disproportion / suspected obstruction.
• Malpresentation unsuitable for the instrument (brow, mento-posterior face, transverse lie).
• Foetal conditions: bone demineralisation disorders (osteogenesis imperfecta), bleeding diatheses (haemophilia, alloimmune thrombocytopenia).
• Live foetus where vaginal delivery is contraindicated.

Vacuum-specific: prematurity <34 weeks, face/brow presentation, foetal coagulopathy/scalp blood-sampling concerns, non-vertex.

Complications

Maternal

• Genital tract trauma: perineal tears (incl. 3rd/4th-degree obstetric anal sphincter injuries, OASIS — higher with forceps), vaginal/cervical lacerations, extension of episiotomy.
• Postpartum haemorrhage.
• Bladder/urethral injury, urinary retention.
• Pain, dyspareunia; rarely vesicovaginal fistula.

Foetal/neonatal — the high-yield trio

Distinguishing the three scalp/skull collections is a classic MCQ.

Feature	Caput succedaneum	Cephalhaematoma	Subgaleal haemorrhage
Plane	Above periosteum (subcutaneous, oedema)	Subperiosteal	Between aponeurosis & periosteum (subaponeurotic)
Crosses suture lines?	Yes	No (limited by sutures)	Yes (spreads widely)
Onset	Present at birth	Hours after birth	Hours, progressive
Fluctuant / shifts?	Pits on pressure	Firm, fixed	Boggy, fluctuant, shifts with position
Danger	Benign, resolves in days	Resolves weeks; jaundice; rare #	LIFE-THREATENING — can hold large blood volume → hypovolaemic shock, anaemia
Association	Normal/prolonged labour	Vacuum > forceps	Vacuum (most feared)

High-yield: Subgaleal haemorrhage is the most dangerous neonatal complication of vacuum delivery — the subaponeurotic space is large and can sequester a neonate's entire blood volume → shock and death. Suspect with a boggy, fluctuant, expanding scalp swelling crossing sutures; monitor haematocrit and resuscitate.

High-yield: Cephalhaematoma does NOT cross suture lines (it is subperiosteal); caput succedaneum and subgaleal bleed DO cross sutures.

Other neonatal injuries:

• Forceps: facial bruising/marks, facial nerve (CN VII) palsy (pressure over stylomastoid foramen), skull fractures, ocular injury.
• Vacuum: retinal haemorrhages (common, usually benign), chignon, scalp lacerations/necrosis, intracranial haemorrhage (rare but serious), hyperbilirubinaemia from scalp bleeds.

Differentials / decision points

• Failed OVD vs proceed to caesarean: if prerequisites are doubtful (station, position, CPD), or after a defined number of failed pulls/pop-offs, abandon and deliver by caesarean. Trial of instrumental delivery should ideally be conducted in theatre when failure is anticipated.
• Choice of instrument: preterm, suspected bleeding disorder, or where rotation is needed and operator skilled → forceps/Kielland's; routine outlet/low with cooperative mother and need to minimise maternal trauma → vacuum.
• Shoulder dystocia must be anticipated after instrumental delivery of a macrosomic infant.

Recently asked / exam angle

• Classification stems: "Scalp visible at introitus, sagittal suture in AP, rotation ≤45°" → Outlet forceps. "Head not engaged" → high station — caesarean, not forceps.
• Prerequisites single-best: "Which is essential before forceps?" → fully dilated cervix / engaged head / empty bladder (commonest distractor set).
• Instrument identification: Piper's → aftercoming head of breech; Kielland's → rotation/deep transverse arrest (no pelvic curve, sliding lock); Wrigley's → outlet/at caesarean.
• Vacuum flexion point: "3 cm anterior to posterior fontanelle on the sagittal suture."
• Complication MCQ: boggy swelling crossing sutures, expanding, shock in neonate after ventouse → subgaleal haemorrhage. Swelling not crossing sutures → cephalhaematoma.
• Contraindication: ventouse at 32 weeks → contraindicated (prematurity).
• Forceps vs vacuum: which causes more maternal perineal trauma (forceps); which causes more cephalhaematoma (vacuum); which allows active rotation (forceps).

Rapid revision

1. Forceps = traction + rotation; vacuum = traction only.
2. Absolute prerequisites: cervix fully dilated, membranes ruptured, head engaged (≤ ischial spines), position known, no CPD, empty bladder, adequate analgesia, consent.
3. High station (unengaged head) = OVD contraindicated → caesarean.
4. Outlet: scalp visible, sagittal suture AP, rotation ≤45°. Mid: engaged but above +2.
5. Kielland's = rotation (no pelvic curve, sliding lock); Piper's = aftercoming head of breech; Wrigley's = outlet.
6. Vacuum flexion point = sagittal suture, 3 cm in front of posterior fontanelle; abandon after 3 pulls / 3 pop-offs / ~15–20 min.
7. Vacuum contraindicated: prematurity <34 wks, face/brow, foetal coagulopathy.
8. Vacuum → more cephalhaematoma & retinal haemorrhage; forceps → more maternal tears & facial nerve palsy.
9. Cephalhaematoma does NOT cross sutures (subperiosteal); caput & subgaleal DO cross sutures.
10. Subgaleal haemorrhage = most dangerous neonatal complication of vacuum → hypovolaemic shock; boggy fluctuant expanding swelling.
11. Avoid sequential instrument use (vacuum→forceps) — high trauma; reassess for caesarean.
12. Facial nerve palsy classically follows forceps (pressure at stylomastoid foramen).