Discuss the use of instrumental delivery in modern obstetrics including forceps, vacuum/ventouse and the Odon device

Clinical overview

Assisted (operative) vaginal birth — delivery of the fetus with forceps or a vacuum (ventouse) — is one of the defining technical skills of the obstetrician. Roughly one in ten births in many settings is assisted vaginally, and the safe, judicious use of these instruments shortens the second stage when continuing to await spontaneous birth would expose mother or fetus to harm, while avoiding a second-stage caesarean with its substantially higher maternal morbidity. The choice is rarely "instrument versus nothing"; it is "instrument now versus caesarean now", and a competent registrar must be able to reason through that decision under time pressure, select the correct instrument, place it correctly, and — critically — know when to stop.

In the South African context this skill is sharpened by resource realities. Second-stage caesarean in a district hospital, often at night with a junior on call, carries real risks of impacted fetal head, extension tears, haemorrhage and delay to theatre. A correctly performed assisted vaginal birth in a woman who fulfils the prerequisites can be the safer option — but only where the operator is trained and the conditions are met. The Saving Mothers (NCCEMD) reports repeatedly highlight that inappropriate or failed instrumental delivery, and delays in escalating to caesarean, contribute to avoidable maternal and perinatal harm. The instrument is only as safe as the judgement behind it. This chapter discusses indications, classification, technique, the three instruments named in the objective (forceps, vacuum, and the newer Odon device), and the framework for safe decision-making. See also Complicated labour, Perineal protection and OASIS.

Core knowledge

Indications

Indications are conventionally grouped, but in practice they overlap and a single judgement integrates them:

• Fetal: a suspicious or pathological CTG in the second stage, or other evidence of fetal compromise where expedited birth is warranted (see CTG interpretation and Fetal monitoring methods).
• Maternal: maternal exhaustion, the need to avoid prolonged Valsalva (e.g. significant cardiac disease, severe hypertension/pre-eclampsia where a controlled second stage is desirable — see Pre eclampsia and HELLP), or a prolonged second stage.
• Inadequate progress in the second stage: definitions of "prolonged" classically allow longer with regional analgesia and for nulliparous women than for multiparous women; standard teaching (and RCOG GTG 26) uses thresholds in the order of active pushing for ~2 hours (nulliparous) or ~1 hour (multiparous), extended further if epidural analgesia is in place. Use local NDoH/unit thresholds.

There is no absolute numerical indication; the decision is clinical. An assisted birth is appropriate only when the benefit of expediting delivery outweighs the risk of the procedure, and when the prerequisites for a safe attempt are met.

The prerequisites — a non-negotiable checklist

Before any attempt, every condition below must be satisfied. A useful structured mnemonic is the components of a full assessment — many units teach a checklist covering the mother, fetus and operator. The essentials:

• Fully dilated cervix (second stage). Instrumental delivery at less than full dilatation is contraindicated outside very specific circumstances.
• Membranes ruptured.
• Vertex (cephalic) presentation with the position and station precisely known by abdominal and vaginal examination. The operator must know exactly where the occiput is and how much caput/moulding is present.
• Engaged head with no more than one-fifth palpable abdominally; the bony station must be at or below the ischial spines (station 0 or lower). A head that is two-fifths or more palpable abdominally is a contraindication.
• Empty bladder (catheterise).
• Adequate analgesia appropriate to the procedure — at minimum effective perineal/pudendal block for low-cavity lift-outs; regional or denser block for rotational or mid-cavity births.
• Adequate maternal pelvis with no suspicion of cephalopelvic disproportion.
• Consent obtained (verbal in the acute setting, documented), the operator trained and competent for the chosen procedure and station, and a clear plan including where the birth will occur and what to do if it fails (see Informed consent).
• Backup available: ability to proceed to caesarean and neonatal resuscitation standing by (see Neonatal resuscitation).

Classification by station and rotation

The internationally used classification (RCOG GTG 26; ACOG) stratifies by how high the head is and how much rotation is needed — this directly determines difficulty, risk and who should perform it: