Macrosomia prediction using ultrasound fetal abdominal circumference of 35centimeters or more

Objective: To determine if birth weights greater than 4000 g can be predict ed by ultrasound measurements of abdominal circumferences. Methods: In 1996, 254 newborns delivered at Tampa General Hospital weighed at least 4000 g, 84 of whom had ultrasound examinations within 2 weeks of d elivery. Those were compared with 84 neonates with recent ultrasounds who w eighed less than 4000 g. Data were abstracted retrospectively from maternal medical records. Results: The best linear predictor of birth weight was ultrasound measureme nt of abdominal circumference (AC), which had a correlation coefficient of 0.95. An AC measurement of 35 cm or more predicted 93% of macrosomic infant s. Among 177 macrosomic infants born vaginally, 23 (13%) had shoulder dysto cia. In that group, induction of labor was associated with a greater than t hree-fold increase in risk of shoulder dystocia (odds ratio [OR] 3.4, 95% c onfidence interval [CI] 1.4, 8.2; P <.01). Labor augmentation was not assoc iated with increased risk of shoulder dystocia. Conclusion: Abdominal circumference measurements were useful in screening f or suspected macrosomia. An AC measurement of 35 cm or more identified more than 90% of macrosomic infants who were at risk for shoulder dystocia. Ind uction of labor in macrosomic patients increased the risk of shoulder dysto cia. (Obstet Gynecol 1999;93:523-6. (C) 1999 by The American College of Obs tetricians and Gynecologists.).