Fetal blood sampling and scalp lactate — structured SAQ (15 marks)

(a) Indications, prerequisites and contraindications (5 marks)

One mark for the indication framed correctly, one for the prerequisites, two for the contraindication list, one for the group B streptococcus exception. ^[1][2]

Indication: a CTG that remains abnormal after reversible causes have been corrected, in a fetus that is not acutely compromised, where birth is not imminent, and where the result will change management.^[1][2]

Prerequisites: ruptured membranes; cervix dilated more than 4 cm; cephalic presentation; informed consent; and a plan for what each result will trigger.^[1]

Contraindications to exclude: ^[1][6]

• Gestation under 34 weeks.
• A CTG suggesting serious sustained compromise, for example bradycardia beyond 5 minutes.
• Known or suspected fetal bleeding disorder — haemophilia, alloimmune thrombocytopenia.
• Non-vertex presentation.
• Maternal HIV, hepatitis B or hepatitis C.
• Active genital herpes lesions.
• Suspected intrauterine sepsis.^[1][6]

The exception in this stem: maternal group B streptococcus colonisation is not a contraindication. State it explicitly.^[1]

(b) Technique (4 marks)

One mark for position with the reason, one for equipment, two for the technical sequence. ^[1][2]

• Position: left lateral (preferred), or lithotomy with a lateral wedge — to avoid aortocaval compression, which can itself worsen the trace.^[1]
• Equipment: amnioscope of appropriate size with light source, swabs, silicone gel or soft paraffin, ethyl chloride spray, guarded blade, heparinised capillary tube with mixing wire and magnet, and a calibrated analyser or lactate meter to hand.^[1][2]
• Sequence: consent and check contraindications aloud; insert the amnioscope and seat it on the scalp, confirming you are not on a fontanelle, the face or the genitalia; clean and dry the scalp; apply gel so blood beads rather than spreads; stab with the guarded blade; collect by capillary action without air bubbles; apply pressure through a contraction until haemostasis; confirm the fetal heart rate; analyse immediately.^[1][2]
• Document: indication, consent, time, result, interpretation, decision, and who you informed.^[1]

(c) Thresholds with their source and actions (4 marks)

One mark per band correctly reproduced for both analytes, one mark for naming the source and the repeat intervals. ^[1][2]

• Source: RANZCOG C-Obs 1 Intrapartum Fetal Surveillance clinical guideline (v5.2, June 2026), as operationalised in ANZ jurisdictional protocols. Either analyte is acceptable.^[1]
• Add the caveat that earns the extra mark: lactate cut-offs are device-specific. The classic threshold above 4.8 mmol/L belongs to a point-of-care meter no longer manufactured; prospective data using the StatStrip system support a cut-off around 5.2 mmol/L. Always state the guideline or the meter with the number.^[5][1]

(d) An abnormal lactate result (2 marks)

One mark for correctly classifying the result and acting, one mark for the parallel actions. ^[1][2]

The result is a lactate of 5.6 mmol/L, which is abnormal on any current threshold.^[1][5]

• Expedite birth. At 6 cm dilatation with a cephalic presentation, that means caesarean section; operative vaginal birth is not available.^[1]
• In parallel: continue intrauterine resuscitation, keep the oxytocin off, call the consultant, alert theatre, anaesthetics and the neonatal team, consent for caesarean, and take paired umbilical cord gases at birth.^[1][2]
• Do not repeat the sample. Do not wait for the consultant to arrive before making the decision.^[1]