Sonographic prediction of fetal macrosomia: the consequences of false diagnosis.

Objective: The purpose of this study was to determine the effect of false diagnosis of macrosomia (<4500 g) on maternal/perinatal outcomes.

Methods: We conducted a case-control study of women (n = 1938) in whom sonographically estimated fetal weight (EFW) was determined up to 3 days before delivery and actual birth weight (BW) was 3500 to 4499 g. Women with false-positive and -negative findings for macrosomia were compared, respectively, with women with true-negative and -positive findings for outcome variables.

Results: The cesarean delivery (CD) rate was 2 to 2.5 times higher when EFW was 4000 to 4499 g, regardless of actual BW. Failure to detect macrosomia was associated with higher rates of perineal trauma, 5-minute Apgar scores less than 7, and neonatal trauma, mostly related to the higher rate of surgical vaginal deliveries. The use of another sonographic model with a lower false-positive rate could theoretically reduce the CD rate by approximately 5%.

Conclusions: False diagnosis of macrosomia substantially increases the CD rate and leads to maternal/neonatal complications.