Some comments on “fetal growth velocity in diabetics and the risk for shoulder dystocia: a case-control study”

Abstract

Dear Editor, We read with interest the recent article by Mirella et al. [1], which presented an interesting study about fetal growth velocity in patients with diabetes and the risk for shoulder dystocia. They reported that fetal growth trajectories were not predictive of an increased risk for shoulder dystocia. Their report, however, raises some questions about the study design and findings. The main purpose of the study was “to determine if fetal growth trajectory measured from sonographic-estimated fetal weight percentiles was associated with an increased risk for shoulder dystocia in pregnancies complicated by diabetes mellitus” [1]. The authors need to describe the reference for EFW according to gestational age that was used to calculate the percentile of each EFW, such as the study by Hadlock et al. [2]. Moreover, we think that the fetal growth trajectory, measured from ultrasonography-estimated fetal weight (US-EFW) percentiles, may help to predict the more accurate EFW in certain situations. For instance, a situation wherein the birth is imminent but the immediate US-exam for EFW is not available and the last US-EFW is outdated. In such a situation, we can presume more accurate EFW from the fetal growth trajectory; moreover, the fetal growth trajectory can help to monitor for large for age (LGA) or macrosomia. If a new US-based EFW is available, then fetal growth trajectory is negligible and the clinician should choose the newer EFW to assess total risk in a particular woman in labor. LGA and macrosomia should also be included as those are well-known risk factors for shoulder dystocia. As this was designed as a case-control study, we doubt whether it is a representative group. The authors described “All the cases of shoulder dystocia occurred at one institution with standardized definitions of shoulder dystocia and that were clinically significant as defined by a quality assurance review process” [1]. Generally, standardized definitions and application of the standardized definitions are very important. However, the fact that the standardized definition was applied could not guarantee the representativeness of the shoulder dystocia cases. Shoulder dystocia show a wide spectrum of outcomes, from normal birth to transient/permanent nerve palsy or even neonatal demise. The majority of shoulder dystocia cases do not involve serious complications, but we are concerned with the minority of the cases that result in neonatal adverse outcomes. We possibly need to categorize shoulder dystocia cases into those with and those without neonatal complications. The shoulder dystocia case group of the study did not have statistically different neonatal adverse outcomes compared with the control group [1]. There was no comment regarding clavicle/humeral fracture or brachial plexus injury in the neonates nor of LGA or macrosomia [1]. We think the authors have been providing good care to pregnant women with diabetes, as evident by the very low neonatal adverse outcome rate. Ironically, this makes it difficult to agree that the study population was appropriate to evaluate the shoulder dystocia cases.