Describe obstetric forceps — its aetiology, clinical features and management.

Definition

Obstetric forceps is a paired instrument designed to grasp the fetal head and assist its delivery by traction (and sometimes rotation). Each blade has a cephalic curve (to fit the head) and a pelvic curve (to fit the birth canal).

Parts

Each branch has a blade (fenestrated), shank, lock and handle; the two branches articulate at the lock.

Types

• Outlet and low forceps — head on the perineum/low cavity (e.g. Wrigley's).
• Mid-cavity / long-handled forceps (e.g. Anderson's, Das).
• Rotational forceps with no pelvic curve (e.g. Kielland's) for malposition.

Prerequisites ("rules" Before Application)

• Cervix fully dilated and membranes ruptured.
• Head engaged, with a known position, and no cephalopelvic disproportion.
• Vertex (or face mento-anterior) presentation; bladder empty; adequate analgesia and aseptic technique.

Functions

The forceps may be used for traction (the commonest use — to extract the head), rotation of a malposition (e.g. Kielland's), and protection of the after-coming head of a breech or a preterm head.

Contraindications

Cephalopelvic disproportion, an unengaged head, a non-fully-dilated cervix, an unknown position, and a malpresentation unsuitable for forceps (e.g. Brow, mento-posterior face).

Indications and Complications

Indications — delay in or a need to shorten the second stage (maternal exhaustion, cardiac/severe pre-eclampsia, fetal distress), after-coming head of a breech. Complications — maternal genital-tract trauma and PPH; fetal facial bruising/nerve palsy, cephalhaematoma and (rarely) skull injury.

A Note on WHY the Preconditions for Forceps Are Absolute

A useful concept is understanding why the prerequisites for forceps delivery are absolute, and why breaking any one of them is dangerous. The forceps grasps the fetal head and delivers it by traction; this is safe only if the head can in fact pass through the pelvis. Hence the classical prerequisites, each preventing a specific disaster: the cervix must be fully dilated (traction against a partly-dilated cervix tears it, causing severe haemorrhage); the membranes must be ruptured and the head engaged with no significant disproportion (pulling on an unengaged head means pulling against an obstruction — causing fetal injury and uterine rupture); the position and station of the head must be known exactly (misapplied blades injure the fetal face, eyes and skull); the bladder must be empty; adequate analgesia must be given; and there must be a valid indication and a readiness to abandon the attempt. Compared with the ventouse, forceps are quicker and more reliable, with a firmer grip — hence their use for fetal distress, the after-coming head of a breech and preterm babies — but they cause more maternal trauma (perineal and vaginal tears), whereas the ventouse causes more fetal scalp trauma and requires maternal effort.

Prerequisites must all be satisfied before application.

• Forceps deliver the head by traction; types: outlet, low and mid-cavity (Kielland's for rotation — now rare).
• Prerequisites: fully dilated cervix, ruptured membranes, engaged head with no disproportion, known position/station, empty bladder, adequate analgesia, valid indication.
• Indications: maternal exhaustion, prolonged second stage, fetal distress, conditions requiring a shortened second stage (heart disease), and the after-coming head of a breech.
• Forceps cause more maternal trauma (tears); the ventouse causes more fetal scalp trauma but less maternal injury.
• Complications: perineal/vaginal/cervical tears, PPH, bladder injury; fetal facial nerve palsy, skull fracture, intracranial haemorrhage.