Ultrasound exams are notoriously inaccurate for predicting the weight of your baby. The ultrasound gives an estimate of the weight of your baby, but this estimate can be off a pound or more in either direction. There are multiple ways to predict the weight via ultrasound, making it not advised for most to make decisions about induction and planned cesarean section based solely on estimated fetal weight.
While it makes patients uncomfortable to think that a) care providers routinely rely on inaccurate measures of fetal weight when making recommendations of the safety of vaginal birth and that b) care provider bias plays a significant role in determining whether or not a woman will have an unnecessary cesarean, Weiss writes briefly about one study that suggests that a bedside ultrasound will increase the chance of surgical birth.
One thing that is show in some studies is that an estimation of a big baby via ultrasound can increase the likelihood that you will have a cesarean. This is thought to be because your practitioner has the “big baby” seed planted in his or her mind already and is less tolerant of variances in labor.