Suspected fetal macrosomia — structured oral station (12 minutes)

Opening prompt — "The scan shows a large-for-dates estimate. How would you counsel her?"

Model response — say it in this order: ^[1][5]

• "First, I would frame the result honestly: the estimated fetal weight is an estimate, not a measurement, and ultrasound formulas carry a roughly 15 percent error margin. A 4250 g estimate could represent a baby of roughly 3600 to 4900 g."
• "The estimate predicts a big baby well but shoulder dystocia poorly — an EFW over 4000 g has a positive likelihood ratio of roughly 8.7 for predicting birthweight macrosomia but only around 2.1 for predicting shoulder dystocia, because most shoulder dystocia occurs in non-macrosomic fetuses."
• "I would then discuss her individual risk factors: she has no diabetes, which is reassuring — diabetes amplifies shoulder dystocia risk at every birthweight. Her previous 3.9 kg vaginal birth is reassuring. Her options are induction at 38 to 39 weeks, expectant management with surveillance, or — only if the estimate is over 5000 g in a non-diabetic — a planned caesarean."
• "I would present the evidence on each and support her in an individualised decision."^[1][2]

Probe 1 — "What does the evidence say about induction?"

• "The Boulvain 2015 Lancet trial randomised 822 women with EFW over the 95th centile to induction at 37 to 38+6 weeks versus expectant management. Induction reduced the composite of shoulder dystocia and associated morbidity — 8 events versus 25, RR 0.32, 95% CI 0.15 to 0.71 — without increasing caesarean and with more spontaneous vaginal births."^[2]
• "The Cochrane 2023 review of four trials and 1190 women confirmed a reduction in shoulder dystocia (RR 0.60, 0.37 to 0.98) and fracture (RR 0.20, 0.05 to 0.79) without a significant effect on caesarean (RR 0.91, 0.76 to 1.09)."^[3]
• "The more recent Gardosi Big Baby 2025 Lancet trial of 2893 women found no significant difference in shoulder dystocia in intention-to-treat — RR 0.75, 95% CI 0.51 to 1.09 — but a reduction in the per-protocol analysis, RR 0.62, 0.41 to 0.92. The trial was terminated early for lower-than-expected shoulder dystocia, which narrowed the difference between groups."^[4]
• "The honest counsel is: induction modestly reduces shoulder dystocia and fracture without increasing caesarean, and the effect is smaller than the early Boulvain trial suggested."^[2][4]

Probe 2 — "When would you offer a planned caesarean?"

• "ACOG Practice Bulletin 216 advises that prophylactic caesarean may be offered for an EFW over 4500 g in diabetic women and over 5000 g in non-diabetic women, reflecting the steep rise in permanent brachial plexus injury at these weights."^[1]
• "Her EFW of 4250 g is below both thresholds — so a caesarean on the estimate alone is not recommended."^[1]

Probe 3 — "She has no diabetes. Why does diabetes change the threshold?"

• "In a non-diabetic fetus the head is the biggest part, so once it delivers the shoulders usually follow. In a diabetic fetus the trunk and shoulders grow disproportionately under fetal hyperinsulinaemia, so a head that delivers can be followed by shoulders that do not."
• "Nesbitt 1998 showed that diabetic women had roughly double the shoulder dystocia rate at every birthweight band — for example, around 35 percent at 4750 to 5000 g in diabetic women versus around 14 percent in non-diabetic women."^[6]
• "That disproportionate shoulder growth is why the ACOG caesarean threshold is lower in diabetes (4500 g) than non-diabetes (5000 g)."^[1]

Probe 4 — "She is worried and asks what you would recommend."

This is a scored communication domain — demonstrate the counsel out loud: ^[1][5]

• "Given your previous uncomplicated vaginal birth, your normal glucose tolerance, and the fact that the estimate could be 3600 or 4900 g, my recommendation is a trial of labour. I would offer induction at 38 to 39 weeks, because it modestly reduces the risk of shoulder dystocia without increasing your chance of a caesarean — but expectant management is also entirely reasonable."
• "I will make sure the team is prepared, that we have rehearsed the manoeuvres for the rare event of shoulder dystocia, and that you and your baby are closely monitored through labour."
• Avoid false reassurance ('it will be fine') and avoid over-intervention ('let us book a caesarean just in case'). Hold the balance.^[1][5]

Probe 5 — "What if shoulder dystocia occurs in labour?"

• "Recognise the turtle sign — the head delivers and retracts against the perineum — and call for help immediately. Begin the manoeuvre sequence: McRoberts (hyperflex the hips) with suprapubic pressure, then rotational manoeuvres (Wood's screw, Rubin), then delivery of the posterior arm, then the all-fours position, and last-resort manoeuvres if needed."
• "Never apply fundal pressure — it is a documented harm. Document the timing, the manoeuvres, the team present, and the neonatal assessment accurately for governance."^[6]