Rates of obesity in the United States (US) have continued to increase over the past several decades, and now obesity affects an estimated 40% of US reproductive-aged women. Pregnant patients with obesity are at increased risk for macrosomia and large for gestational age neonates, which in turn increases the risk for obstetrical complications such as shoulder dystocia and cesarean delivery. Previous studies have demonstrated that obese women have larger estimated fetal weights (EFW) and fetal abdominal circumference (AC) measurements compared with normal weight women. Additionally, regardless of maternal weight, impaired glucose tolerance and gestational diabetes (GDM) have been associated with larger EFW and fetal AC. Notably, both large EFW and large AC have independently been associated with increased risk of LGA, macrosomia, and shoulder dystocia. Given the overlapping processes in obesity and diabetes that contribute to fetal overgrowth, we suspect that severe obesity and impaired glucose tolerance have an additive effect on risk of fetal overgrowth. However, there is a lack of data on fetal growth trajectory in women with class III obesity, and the contribution of impaired glucose tolerance and GDM to fetal overgrowth in this population is not well-studied. The purpose of this study is to compare fetal growth parameters during the second and third trimester in the class III obese population, based on glucose tolerance status.

We conducted a retrospective cohort study of pregnancies delivered at Oklahoma Children's Hospital at OU Health from 10/22/2020-11/30/2025. Inclusion criteria: singleton gestation, BMI ≥ 40 at the initial prenatal visit, ultrasound (US) exam prior to 22 weeks, completed glucose screening, and delivery at ≥34 weeks. Exclusion criteria: stillbirth, known major fetal anomaly, and major maternal medical comorbidities. Fetal US biometric parameters were collected and analyzed across 5 time periods (22-25 weeks, 26-29 weeks, 30-33 weeks, 34-37 weeks, and 38 weeks and beyond). Outcomes were analyzed between three groups based on glucose tolerance status: normal glucose tolerance (NGT), impaired glucose intolerance (IGT; defined as hemoglobin A1c 5.7-6.4% prior to 20 weeks and/or one abnormal value on the 100-gram 3-hour glucose tolerance test), or GDM. The primary outcomes were difference in EFW and AC percentile on late third trimester ultrasound (34-37 weeks) between the three groups. Secondary outcomes consisted of maternal and neonatal outcomes including rates of shoulder dystocia, cesarean delivery, LGA, macrosomia, and a composite of neonatal adverse outcomes.

Of 19,770 deliveries during the study period, 711 pregnancies met inclusion criteria. On US performed at 34-37 weeks,the EFW percentile was significantly greater in women with IGT and GDM compared to women with NGT (NGT 27.1% vs IGT 59.9% vs 68.1%, p<0.0001). Women with IGT and GDM also had a significantly higher rate of fetal AC ≥ 90^th %ile (NGT 20.9% vs IGT 32.8% vs GDM 41%, p<0.0001) and fetal AC ≥97%ile (NGT 6.8% vs IGT 9.0% vs GDM 19.0%, p=0.0005). Mode of delivery was similar between groups, however shoulder dystocia was more common in women with GDM (NGT 0.8% vs IGT 0% vs GDM 5.5%, p<0.0019). LGA was more common in women with IGT and GDM (NGT 13.1% vs IGT 24.4% vs GDM 39.1%, p<0.0001), as was macrosomia (NGT 6.95 vs IGT 14.1% vs GDM 18.8%, p<0.0001). The rate of the composite neonatal adverse outcome was highest in the GDM group (NGT 23.0% vs IGT 20.5% vs GDM 56.3%, p<0.0001).

Our study illustrates the additive effects of IGT and GDM on risk of fetal overgrowth and related adverse perinatal outcomes in women with severe obesity. In particular, the rate of large fetal AC, which is an independent predictor of LGA, macrosomia, and shoulder dystocia, increases with worsening glucose tolerance. These findings highlight the necessity of counseling patients with severe obesity (either with normal or abnormal glucose tolerance) on pregnancy risks related to fetal overgrowth, and the importance of finding clinical interventions to ameliorate the impact of these conditions on fetal growth.