Ultrasonographic prediction of fetal macrosomia - Association with cesarean delivery

OBJECTIVE: To investigate whether the incorrect ultrasonographic prediction of macrosomia affects the cesarean delivery rate among non-macrosomic neon ates. STUDY DESIGN: For this retrospective, cohort study, comprehensive ultrasono graphic records were reviewed oed at two centers. Patients with singleton, nonanomalous gestations whose ultrasonography predicted an estimated fetal weight greater than or equal to 4,000 g composed one cohort (n = 135), whil e the other cohort (n = 129) consisted of patients whose ultrasonography pr edicted an estimated fetal weight be tween 3,000 and 3,999 g. We compared t he cesarean de livery rate in neonates falsely diagnosed with macrosomia (f alse positives) with the rate in those correctly diagnosed as nonmacrosomic (true negatives). RESULTS: The rate of cesarean delivery was significantly higher among those falsely diagnosed by ultrasonography with a macrosomic fetus as compared t o those with a fetus truly diagnosed as non macrosomic (42.3% vs. 24.3%, re lative risk=1.74, 95% confidence interval 1.09-2.78). Subgroup analyses exc luding diabetic mothers and multiparous women and comparing false positives with true negatives with neonatal birth weights between 3,500 and 4,000 g (birth weights similar to false positives) demonstrated significantly incre ased cesarean delivery rates among false positives. CONCLUSION: Even in nonmacrosomic neonates, the antenatal ultrasonographic diagnosis of suspected macrosomia is associated with a significant increase in is associated with a significant increase in cesarean delivery rates.