From the Guidelines
The estimated fetal weight at which an ultrasound is deemed accurate enough to predict shoulder dystocia risk and consider a c-section is typically above 4500g for diabetic mothers and above 5000g for non-diabetic mothers, but this should not be the sole determinant for cesarean delivery. When considering the risk of shoulder dystocia, it's essential to take into account multiple factors, including maternal diabetes status, history of shoulder dystocia, maternal pelvic measurements, and labor progression 1. According to the American College of Obstetricians and Gynecologists, suspected fetal macrosomia is not an indication for induction of labor, and labor and vaginal delivery are not contraindicated for women with estimated fetal weights up to 5,000 g in the absence of maternal diabetes 1.
Key Considerations
- The decision for cesarean delivery should be individualized and based on multiple factors, not solely on estimated fetal weight.
- For diabetic mothers, consideration of cesarean may begin at EFW >4500g, while for non-diabetic mothers, the threshold is often higher at >5000g.
- Most cases of shoulder dystocia occur in babies weighing less than 4500g, and most large babies deliver without complications.
- Ultrasound accuracy diminishes with increasing fetal size, making it an imperfect tool for predicting this complication.
Recommendations
- The American College of Obstetricians and Gynecologists recommends individualized decision-making rather than using EFW as the sole determinant for cesarean delivery.
- A prolonged second stage of labor or arrest of descent in the second stage is an indication for cesarean delivery, especially with an estimated fetal weight more than 4,500 g 1.
- The risk-benefit discussion should include potential surgical complications versus the relatively low risk of permanent injury from shoulder dystocia.
From the Research
Estimated Fetal Weight and Shoulder Dystocia Risk
- The estimated fetal weight at which an ultrasound is deemed accurate enough to predict shoulder dystocia risk is not explicitly stated in the provided studies for a 36-week ultrasound.
- However, according to the study by 2, cesarean delivery is recommended before labor in cases of estimated fetal weight (EFW) >4500g if associated with maternal diabetes, and EFW >5000g in women without diabetes.
- Another study by 3 analyzed the effectiveness and costs of elective cesarean delivery for fetal macrosomia diagnosed by ultrasound, considering policies with estimated fetal weight thresholds of 4000g and 4500g.
- The study by 3 found that for nondiabetic women, the 4500-g policy would require 3695 cesarean deliveries to prevent one permanent brachial plexus injury, at an additional cost of $8.7 million.
Prediction and Management of Shoulder Dystocia
- Shoulder dystocia is a complication of vaginal delivery and the primary factor associated with brachial plexus injury, as discussed in the study by 4.
- The study by 2 recommends induction of labor in cases of impending macrosomia if the cervix is favorable at a gestational age of 39 weeks or more, and cesarean delivery in certain situations, including estimated fetal weight >4500g with maternal diabetes, and estimated fetal weight >5000g without diabetes.
- The study by 5 suggests that macrosomia and subsequent shoulder dystocia cannot be predicted, and that great clinical acumen and technical expertise by the obstetrician are necessary to avoid injury to the mother and fetus when shoulder dystocia occurs.
Considerations for Cesarean Delivery
- The study by 6 discusses the impact of cesarean section on request at 39 weeks on shoulder dystocia, fetal trauma, neonatal encephalopathy, and intrauterine fetal demise, and suggests that cesarean delivery may be protective for the development of neonatal encephalopathy.
- The study by 3 found that for diabetic women, a policy of elective cesarean delivery for ultrasonographically diagnosed fetal macrosomia appears to be more tenable, although the merits of such an approach are debatable.