Maternal obesity
Description
- BMI >=30 kg/m2 at booking (WHO classes I-III)
- Independent risk factor across essentially every pregnancy complication
- Prevalence rising - now one of the commonest high-risk antenatal presentations
Epidemiology
- ~20-25% of pregnant Australian women overweight/obese at booking; obesity alone ~20%
- Class III obesity (BMI >=40) carries the highest complication rates
Aetiopathogenesis
- Chronic low-grade inflammation + insulin resistance -> compounds pregnancy-induced insulin resistance -> inc GDM risk
- Adipose-derived inflammatory mediators -> endothelial dysfunction -> inc pre-eclampsia risk
- Mechanical - inc intra-abdominal pressure, reduced diaphragmatic excursion, obstructive sleep apnoea
- Technical - ultrasound and fetal monitoring accuracy reduced by body habitus; epidural/spinal and surgical access more difficult
Diagnosis
- Booking BMI calculated from measured (not self-reported) height/weight
- Screen early and often for associated conditions:
- Early OGTT if BMI >=35 (or per local ADIPS-aligned protocol) + repeat at 24-28 weeks
- BP at every visit - baseline pre-eclampsia risk assessment
- Consider screening for obstructive sleep apnoea if suggestive symptoms
- Third-trimester growth scan reasonable in Class III obesity even without another indication - clinical palpation/SFH unreliable
Management
Antenatal
- Avoid stigmatising language ("morbid obesity") - use BMI/class terminology
- Dietitian referral, supervised physical activity (30-45 min brisk walk most days is safe)
- Gestational weight gain targets (IOM, by pre-pregnancy BMI)
| Pre-pregnancy BMI | Total recommended gain |
|---|---|
| Normal (18.5-24.9) | 11.5-16 kg |
| Overweight (25-29.9) | 7-11.5 kg |
| Obese (>=30) | 5-9 kg |
- High-dose folate (5 mg) preconception/1st trimester - obesity independently raises neural tube defect risk
- Vitamin D consideration - deficiency more common
- Aspirin prophylaxis if BMI is a contributing risk factor per local pre-eclampsia risk calculator
- Anaesthetic antenatal referral for Class II-III obesity - anticipate difficult airway/epidural access
Intrapartum
- Higher induction and caesarean rates - individualise mode of birth planning
- VTE risk assessment + consider prophylactic LMWH (obesity is a major independent VTE risk factor)
- Early epidural siting reasonable given technical difficulty if labour progresses
- Senior obstetric/anaesthetic input for caesarean - wound and airway planning
Postpartum
- Continue VTE prophylaxis per risk assessment (often extended course)
- Wound care - higher infection/dehiscence risk after caesarean
- Breastfeeding support (initiation rates lower) and postpartum weight management
Associations
- GDM, pre-eclampsia, hypertensive disorders
- Miscarriage, congenital anomaly (esp. neural tube defects), macrosomia
- Induction of labour, prolonged labour, shoulder dystocia, caesarean section
- VTE, wound infection, postpartum haemorrhage
- Obstructive sleep apnoea, difficult airway/regional anaesthesia access
- Stillbirth (dose-dependent with BMI)
Natural history & complications
- Complication rates rise progressively with BMI class, greatest in Class III
- Postpartum weight retention common - inc risk with subsequent pregnancies and long-term cardiometabolic disease
- Preconception weight optimisation is the single most effective intervention - discuss at every reproductive-age contact
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