Prediction of fetal macrosomia using humeral soft tissue thickness

Objective: To determine the usefulness of an objective assessment of humeral soft tissue thickness in estimating birth weight in a population at risk for macrosomia. Methods: Shortly before delivery, ultrasound examinations were performed on 95 women at risk of having macrosomic infants. In each case, the fetal humeral soft tissue thickness (the distance between the outer edge of the humerus to the skin surface on transverse views of the upper arm) was measured three times, and an average was taken. Results: The humeral soft tissue thickness correlated significantly with birth weight (R² = 0.40, P < .001) and ponderal index (R² = 0.20, P = .02). The humeral soft tissue thickness was significantly higher in macrosomic infants (P < .001), in those with an abnormally high ponderal index (P = .02), and in infants whose deliveries were complicated by shoulder dystocia (P = .05). There was no apparent effect of maternal diabetes on the humeral soft tissue thickness. The humeral soft tissue thickness was more sensitive in predicting macrosomia than was the ultrasound-estimated fetal weight (88 versus 71%), but less specific (75 versus 91%). Conclusion: The humeral soft tissue thickness correlates with birth weight. However, its clinical use compared with other predictors remains to be defined.