Obesity in pregnancy — structured SAQ (15 marks)

(a) The booking bundle, with reasoning (5 marks)

One mark per point, maximum five. [1][2]

• Measure (do not ask) weight and height and calculate BMI. Self-reported weight underestimates BMI by one to two units and can drop a class III woman into class II, missing her anaesthetic referral. [1]
• Blood pressure with an appropriately sized cuff. A standard cuff over-reads by 5 to 10 mmHg in obesity and over-diagnoses hypertension; document the cuff size. [1]
• Anaesthetic referral. At BMI above 35 in level 2 or 3 services, BMI above 35 with comorbidity in level 4 or 5 services, or BMI 40 and above in any service (RANZCOG C-Obs 49). She is BMI 36 with PCOS — refer. The aim is to plan the difficult airway, regional technique and venous access weeks before labour; failed intubation is roughly eight times more common in obesity. [1][2]
• VTE risk score at booking, in the chart, and reassessed at every admission and at delivery; obesity is the most powerful single risk modifier. [1]
• Early glucose workup and a 75 g OGTT at 24 to 28 weeks; STOP-BANG or equivalent OSA screen; blood-borne virus and routine antenatal bloods. [1][2]

(b) Vitamin D and aspirin — dose, threshold, rationale (3 marks)

One and a half marks each. [1][9]

• Vitamin D 1000 IU (25 micrograms) cholecalciferol daily from booking through lactation. Twice the routine 400 IU because vitamin D is sequestered in adipose tissue; RCOG Green-top Guideline No. 72 specifies the dose in BMI 30 and above, with safety supported by the Cochrane review. [1][9]
• Aspirin 150 mg nocte from 12 weeks until 36 weeks, because BMI above 35 with one other risk factor (her PCOS and family history of diabetes contribute risk) meets the preeclampsia-prevention threshold. The 150 mg dose, not the legacy 75 mg, is the prevention dose — it restores the prostacyclin-thromboxane balance that obesity-related endothelial dysfunction disrupts. [1]

(c) Fetal growth surveillance (3 marks)

One mark each for the pitfall, the intervention, and the stillbirth context. [1][3]

• The fundal height is unreliable above BMI 30 — the uterus sits deep in an obese abdominal wall and the apparent height is spuriously small or large. Replace the tape measure, do not add it. [1]
• Serial growth ultrasound every 3 to 4 weeks from 28 weeks, plotted on a customised (Growth or INTERGROWTH-21st) chart. This is the standard of care above BMI 30. [1]
• Context: stillbirth is doubled in obesity (Chu 2007 OR 2.07 obese), and reduced fetal movements must be investigated with the same urgency as in any woman — never reassured away as 'expected in obesity'. [3]

(d) VTE prophylaxis at caesarean, with trial evidence (4 marks)

One mark for the dose, one for the route and frequency, two for the trial evidence. [5][6]

• Weight-based enoxaparin 0.5 mg/kg subcutaneously twice daily is the trial-tested dose in the obese post-caesarean woman — not fixed-dose 40 mg. [5][6]
• Overcash 2015 (Obstet Gynecol): 42 morbidly obese (BMI 40 and above) post-caesarean women on 0.5 mg/kg twice daily achieved prophylactic anti-Xa in 86 percent, versus 26 percent on BMI-stratified dosing; no level reached the 0.6 IU/mL therapeutic threshold. [5]
• Stephenson 2016 (J Perinatol, RCT): 84 women with BMI 35 and above, 42 per arm. Weight-based 0.5 mg/kg twice daily achieved prophylactic anti-Xa in 88 percent versus 14 percent on fixed-dose 40 mg daily; no anti-Xa exceeded 0.48 IU/mL. [6]
• Translation: fixed-dose and BMI-stratified regimens under-dose around three-quarters of obese women and leave them unprotected in the highest-risk window. Continue for at least 10 days post-caesarean in BMI above 30, extended to 6 weeks in BMI above 40 or with added risk. [5][6]