Sonographic Findings Associated With Gestational Diabetes in Pregnancies Not Identified by Standard Screening

Objective: To assess the prevalence of gestational diabetes mellitus (GDM) in women without a prior GDM diagnosis who presented with third-trimester sonographic findings of estimated fetal weight (EFW) >90%, abdominal circumference (AC) >95%, or polyhydramnios. Study Design: Between 2018–2023, a perinatal diabetes registry tracked pregnant patients >28 weeks gestation with sonographic findings of EFW >90%, AC >95%, or polyhydramnios (AFI >25 cm), but no prior GDM diagnosis. These patients underwent a third-trimester 3-hour glucose tolerance test (GTT) or glucose panel. The primary outcome was new diagnosis of GDM; secondary outcomes included delivery mode, live birth, shoulder dystocia, respiratory distress syndrome (RDS), preeclampsia, neonatal hypoglycemia, and NICU admission. Results: Of 723 patients, 169 (23.4%) were newly diagnosed with GDM. Among those with specific sonographic findings, GDM was identified in 25.4% (EFW >90%), 24.4% (AC >95%), and 21.2% (polyhydramnios). GDM was diagnosed in 19.5% with one sonographic finding, 25.5% with two, and 26.9% with all three. New third-trimester GDM was significantly associated with increased neonatal hypoglycemia (30.4%; p<.001), RDS (10.8%; p=.037), and NICU admission (13.4%; p=.036). Conclusion: Up to one in four women with third-trimester findings of EFW >90%, AC >95%, or polyhydramnios—despite a prior negative screen—were newly diagnosed with GDM. These cases were also linked to higher neonatal morbidity. Targeted third-trimester GDM screening in patients with these sonographic markers may help identify at-risk pregnancies and improve perinatal outcomes.