Reducing Birth Injuries Associated with Macrosomia

Abstract & Commentary

Synopsis: Induction of labor for suspected macrosomia at term does not reduce the rate of cesarean delivery or traumatic injury to the fetus.

Source: Gonen O, et al. Obstet Gynecol 1997;89: 913-917.

A prospective, randomized study was conduct- ed to determine whether induction of labor would reduce shoulder dystocia, brachial plexus injury, or other morbidities in patients whose fetal weight was estimated to be 4000-4500 g, by ultrasound. Patients with diabetes mellitus, a prior cesarean delivery, or a nonvertex presentation were excluded. Of 273 eligible patients, 134 were randomized to induction of labor (group I) and 139 to expectant management (group II). Patients randomized to expectant management delivered within five days of entering the study. Their babies were significantly heavier, 4132 g vs. 4062 g in group I, respectively. The cesarean delivery rates were not significantly different—19.4% in patients who underwent induction as compared to 21.6% in patients managed expectantly. Overall, 11 deliveries were complicated by shoulder dystocia—five in group I and six in group II. No brachial plexus injuries associated with shoulder dystocia were observed.

Gonen and colleagues conclude that induction of labor for suspected macrosomia at term does not reduce the rate of cesarean delivery or traumatic injury to the fetus and, therefore, an estimated fetal weight between 4000-4500 g should not be an indication for induction of labor.

COMMENT BY STEVEN G. GABBE, MD

In an effort to reduce birth injury in the fetus thought to be macrosomic, some have advocated induction of labor, recognizing that the risks of a failed induction in this setting may offset the benefits of delivering the fetus before it grows any larger. The starting point for this strategy is usually an ultrasonic estimate of fetal weight greater than 4000 g. While ultrasound estimates of fetal weight may be valuable in ruling out macrosomia, the positive predictive value and sensitivity of this technique is approximately 60%. This prospective, randomized investigation reveals that the induction of labor in patients at term whose fetus is suspected to weigh 4000- 4500 g will neither reduce the cesarean delivery rate nor the risk of birth trauma. It should also be noted that patients in the expectant group were delivered within one week of randomization and, while their babies were larger, the difference in weight was only 70 g. Gonen et al report that the study had adequate power to detect an increase or decrease of 15% in the cesarean delivery rate. The study excluded patients with diabetes mellitus and that any woman whose fetus was estimated to weigh more than 4500 g had a cesarean delivery.