Contraindications for Vaginal Delivery Based on Estimated Fetal Weight
Vaginal delivery is not contraindicated for women with estimated fetal weights up to 5,000g in non-diabetic women, but prophylactic cesarean delivery should be considered when estimated fetal weight exceeds 5,000g in non-diabetic women or 4,500g in diabetic women. 1, 2
Specific EFW Thresholds for Delivery Planning
Non-Diabetic Women:
- EFW up to 5,000g: Vaginal delivery is appropriate and not contraindicated 1
- EFW > 5,000g: Consider prophylactic cesarean delivery 1, 2
- EFW > 4,500g with prolonged second stage or arrest of descent: Cesarean delivery indicated 1
Diabetic Women:
- EFW up to 4,500g: Vaginal delivery may be attempted 1, 2
- EFW > 4,500g: Consider prophylactic cesarean delivery 1, 2, 3
Clinical Decision Points During Labor
- Midpelvic arrest with suspected macrosomia: Cesarean delivery should be performed (except in extreme emergencies) 1
- Prolonged second stage with EFW > 4,500g: Indication for cesarean delivery 1
- Midpelvic operative vaginal delivery: Should be avoided with suspected macrosomia 2
Risk Assessment
Risks of Vaginal Delivery with Macrosomia:
- Shoulder dystocia: Risk increases to 9.2-24% when birth weight exceeds 4,500g in non-diabetic women 1, 2
- Brachial plexus injury: 18-21 fold increased risk with birth weight >4,500g 2
- Clavicular fracture: 10-fold increased risk with macrosomia 1
- Maternal lacerations: Higher incidence with vaginal delivery of macrosomic infants 4
Important Caveats:
- Diagnostic imprecision: The diagnosis of fetal macrosomia is imprecise; ultrasound biometry is no better than clinical palpation (Leopold's maneuvers) 1, 2
- Unpredictable complications: Shoulder dystocia can occur unpredictably even in infants of normal birth weight 1, 2
- Cesarean delivery limitations: Cesarean delivery reduces but does not eliminate the risk of birth trauma 1, 2
Labor Management Considerations
- Induction of labor: Not recommended for suspected macrosomia alone, as it may double the risk of cesarean delivery without reducing shoulder dystocia or newborn morbidity 1, 2
- VBAC: Suspected fetal macrosomia is not a contraindication to attempted vaginal birth after a previous cesarean delivery 1
- Cesarean incision: If cesarean delivery is performed for suspected macrosomia, the incision should be large enough to avoid difficult abdominal delivery 1
Cost-Effectiveness Considerations
To prevent a single case of permanent brachial plexus injury at the 4,500g threshold, approximately 155-588 cesarean deliveries would be required 5, which explains why prophylactic cesarean is not recommended until higher weight thresholds are reached.
The evidence clearly supports allowing trials of labor for most cases of suspected macrosomia, with specific weight thresholds guiding when cesarean delivery should be considered to optimize maternal and neonatal outcomes.