Fetal growth velocity in diabetics and the risk for shoulder dystocia: a case-control study

Shoulder dystocia complicates up to 3% of vaginal births. The clinical ability to predict shoulder dystocia is limited, especially among diabetic women. We sought to evaluate if fetal growth trajectory measured from ultrasonographic (US) estimated fetal weight (EFW) percentiles was associated with increased risk for shoulder dystocia.

We performed a case-control study among women diagnosed with diabetes at a single institution between 2005 and 2015. Two diabetic controls without shoulder dystocia based on the year of delivery were included for each woman with a shoulder dystocia. Women with a single EFW measurement, delivery by cesarean, or multiple gestation were excluded. Demographic and US data were collected. Fetal growth trajectory was calculated from EFW measurements in the last two growth ultrasound scans performed closest to delivery. We compared the odds of EFW percentile change per week above specific thresholds for shoulder dystocia cases versus controls. The following cutoffs were generated: a mean percentile per week increase of > 0%, ≥ 0.5%, ≥ 1%, and ≥ 2%. Among those with EFW percentile changes that decreased (<0%), we evaluated whether odds of an abdominal circumference (AC) > 75th percentile or an EFW > 75th percentile was higher for women with shoulder dystocia. The primary exposure was increased growth trajectory. Secondary outcomes included analysis of the following adverse neonatal outcomes: (i) low 5 minutes Apgar score, (ii) rates of NICU admission, and (iii) neonatal demise.

Of 3954 diabetics, we identified 68 cases with shoulder dystocia and 136 controls who did not have shoulder dystocia. Women who experienced a shoulder dystocia were more likely to be of advanced maternal age as compared to those without a shoulder dystocia (41.9% versus 23.5, p = .01); all other demographic characteristics were similar between groups. At growth trajectory cutoffs of > 0%, ≥ 0.5%, ≥ 1%, and ≥ 2% per week, odds ratios were increased among shoulder dystocia cases versus controls (OR = 1.8, 95% confidence interval (CI) = 0.9-3.3; OR = 1.6, 95% CI = 0.8-3.2; OR = 1.7, 95% CI = 0.7-3.9; and OR = 1.8, 95% CI = 0.6-5.3; respectively); however, this was not statistically significant. For women with fetal growth trajectories that decreased (< 0%), shoulder dystocia was associated with increased odds of fetal AC > 75th percentile and overall growth > 75th percentile (OR = 3.3, 95% CI = 1.5-7.1, OR = 4.8, 95% CI = 1.3-17.4, respectively). There was no difference in neonatal outcomes between shoulder dystocia cases and controls.

Future research is required to determine if fetal growth velocity proves to be a useful tool in identifying women at increased risk for shoulder dystocia. Larger studies are required for precise estimates of risk, and associated neonatal outcomes.