Management of Fetal Macrosomia
Labor and vaginal delivery are safe and recommended for estimated fetal weights up to 5,000 g in non-diabetic women and up to 4,500 g in diabetic women, with prophylactic cesarean delivery considered only above these thresholds. 1
Diagnostic Accuracy and Limitations
- Ultrasound estimation of fetal weight is no more accurate than clinical palpation (Leopold's maneuvers) for diagnosing macrosomia 2, 1
- The accuracy of weight estimation is particularly poor in diabetic pregnancies, with standard deviations of 12.2-13.1% compared to the general population 3
- Despite limited accuracy, estimated fetal weight >4,000 g has 77% likelihood of actual macrosomia, and >4,500 g has 86% likelihood 3
- Abdominal circumference at 36 weeks is the single best ultrasound predictor of macrosomia, with 76.5% accuracy 4
- Combining HbA1c measurements (at booking, 14,20, and 36 weeks) with abdominal circumference and anterior abdominal wall thickness improves prediction to 80.9% 4
Maternal Glucose Control and Weight Management
- Excessive weight gain during pregnancy is associated with fetal macrosomia 2
- Regular blood glucose monitoring is essential for both gestational and pre-existing diabetes 5
- Serial fetal growth evaluations should be performed every 4 weeks in diabetic patients to monitor for macrosomia 5
- Women with pre-existing diabetes should ideally receive care in a multidisciplinary clinic 5
Delivery Timing
- Do not induce labor solely for suspected macrosomia, as induction doubles the cesarean delivery risk without reducing shoulder dystocia or improving neonatal outcomes 2, 1
- Randomized trials demonstrate similar cesarean rates (19.4% vs 21.6%) and shoulder dystocia rates between induction and expectant management groups 2, 1
- Avoid elective induction before 39 weeks due to neonatal respiratory complications 1
Mode of Delivery: Algorithm Based on Estimated Fetal Weight
Non-Diabetic Pregnancies:
- EFW <5,000 g: Trial of labor is safe and recommended 2, 1
- EFW ≥5,000 g: Consider prophylactic cesarean delivery 2, 1
- Large cohort studies confirm safety of vaginal delivery for weights >4,000 g 2, 1
Diabetic Pregnancies:
- EFW <4,500 g: Trial of labor is appropriate 1
- EFW ≥4,500 g: Consider prophylactic cesarean delivery 2, 1
- The risk of shoulder dystocia increases dramatically to 19.9-50% when birth weight exceeds 4,500 g in diabetic pregnancies 1, 5
Intrapartum Management
- With prolonged second stage or arrest of descent in the second stage when EFW >4,500 g, proceed to cesarean delivery 2
- Avoid midpelvic operative vaginal delivery except in extreme emergencies; perform cesarean delivery for midpelvic arrest with suspected macrosomia 2
- If cesarean delivery is performed, ensure the incision is large enough to avoid difficult abdominal delivery 2, 1
- Prepare for shoulder dystocia management, as it occurs in 1.4% of all vaginal deliveries but increases to 9.2-24% in non-diabetic women and 19.9-50% in diabetic women when birth weight exceeds 4,500 g 1, 5
Risk Counseling
- Counsel patients about the 10-fold increased risk of clavicular fracture when birth weight exceeds 4,500 g 1
- Inform patients of the 18-21-fold increased risk of brachial plexus injury at this birth weight 1, 6
- Maternal risks include increased cesarean delivery rates, postpartum hemorrhage, and vaginal lacerations 5, 7
Postpartum Monitoring
- All women undergoing cesarean delivery should receive sequential compression devices starting before surgery and continuing until fully ambulatory to prevent venous thromboembolism 5
- Women with gestational diabetes require long-term follow-up, as infants are at increased risk of obesity during adolescence and type II diabetes later in life 7
Critical Pitfalls to Avoid
- Do not rely solely on ultrasound for weight estimation; it performs no better than Leopold's maneuvers 2, 1
- Do not perform prophylactic cesarean for suspected macrosomia <5,000 g in non-diabetic women or <4,500 g in diabetic women, as cost-effectiveness data do not support this approach 2, 1
- Suspected fetal macrosomia is not a contraindication to attempted vaginal birth after previous cesarean delivery 2