Instrumental vaginal birth — structured SAQ (15 marks)

(a) Prerequisites, with the reason for each (5 marks)

Half a mark for each prerequisite, half a mark for the reason, to a maximum of five. ^[1][2]

Bonus credit for naming the assessment itself: fifths palpable abdominally first, then dilatation, membranes, station, position, caput and moulding vaginally. ^[1]

(b) Resolving the uncertain position (3 marks)

• Re-examine deliberately with the woman comfortable, seeking the sagittal suture, both fontanelles and an ear if necessary; caput plus and moulding plus make purely digital assessment unreliable.^[1]
• Perform a transabdominal ultrasound to define the position before any instrument is applied.^[4]
• Quote the evidence: in the IDUS randomised trial of 514 nulliparous women, ultrasound reduced incorrect diagnosis of fetal head position from 20.2% to 1.6% (odds ratio 0.06) without prolonging the decision-to-delivery interval.^[4]
• State the limitation honestly: the same trial showed no reduction in maternal or neonatal morbidity, failed instrumental birth or caesarean. Knowing the position is necessary, not sufficient.^[4]

(c) Setting and instrument (4 marks)

• Setting (1 mark): this is a mid-cavity rotational birth in a nullipara with a pathological trace. Conduct it as a trial of instrumental birth in theatre with the block extended, the team scrubbed, caesarean instruments open, a paediatrician present and the abandonment point stated aloud beforehand.^[1][2]
• Rotation (1 mark): the options are manual rotation followed by non-rotational forceps, rotational vacuum, or Kielland rotational forceps. In a prospective cohort of 381 nulliparous women, postpartum haemorrhage, severe perineal tears, low cord pH, neonatal trauma and nursery admission were comparable across all three; sequential instrument use occurred in 36.9% of rotational vacuum births versus 0.6% after manual rotation with forceps.^[5]
• Instrument trade-off (2 marks): pooled across 31 trials and 5754 women, forceps were less likely to fail (risk ratio 0.58) but caused more third- or fourth-degree tears (risk ratio 1.83) and more reported pain; vacuum caused more fetal scalp trauma including cephalhaematoma and retinal haemorrhage. Rigid cups fail less often than soft cups (risk ratio 1.62 for failure with soft cups).^[3]
• State the stop rules before you pull: no descent with the first correctly applied pull, no birth after three pulls, two cup detachments, or about 20 minutes. Do not swap instruments — sequential vacuum then forceps carried intracranial haemorrhage risk ratio 3.9 and facial nerve injury risk ratio 13.3 compared with spontaneous birth.^[1][8]

(d) Immediate post-procedure management (3 marks)

• Third stage and haemostasis: active management, uterine tone check, quantified blood loss.^[1]
• Systematic genital tract examination including a rectal examination in every case; classify and repair any obstetric anal sphincter injury correctly. Mediolateral episiotomy at 60 degrees from the midline is protective, with odds ratio 0.11 for sphincter injury at vacuum and 0.08 at forceps birth.^[1][7]
• A single dose of intravenous amoxicillin with clavulanic acid — ANODE randomised 3427 women and reduced confirmed or suspected infection at six weeks from 19% to 11% (risk ratio 0.58).^[6]
• Bladder care with timed voiding and post-void residual measurement; thromboprophylaxis assessment; analgesia; paired cord gases; neonatal scalp examination with a documented subgaleal surveillance plan after any vacuum.^[1]
• Documentation and debrief: indication, prerequisites, station, position, instrument, number of pulls, timing, episiotomy, tears, blood loss, and an offer of a debrief before discharge.^[1]