(268) Hemoglobin A1C versus 50g OGTT for Diabetes Screening in Early Pregnancy

Screening for early GDM or undiagnosed type 2 DM is recommended for pregnant patients meeting high risk criteria, but the ideal screening test is unknown. Traditional oral glucose challenge testing requires glucose load prior to lab draw which requires additional clinic and staff time and may be declined by patients. We hypothesized that screening completion rates would be higher with HgbA1C as the initial DM screen versus GTT.

Study Design:
Our clinical protocol for early pregnancy DM screening for high risk patients changed in 2022 from 50g GTT followed by 100g 3hr GTT if >140, to HgbA1C. Patients with HgbA1C >6.4 were diagnosed with DM. Patients with HgbA1C 5.9-6.4 underwent 3hr GTT. Patients with HgbA1C< 5.9 screened negative for early DM. Carpenter-Coustan criteria were used for 3hr GTT. We performed a retrospective cohort study of all patients meeting criteria for early DM screening for 1 year pre- and post- protocol implementation. Primary outcomes included completion of DM screening prior to 20 weeks and time between OB intake and screening completion. Secondary outcomes included proportion of each cohort diagnosed by early versus routine GDM screening and obstetric and neonatal outcomes for each screening cohort.

Results:
1656 patients were included in this study (840 under GTT screening protocol, 816 under HgbA1C screening protocol. 89.7% of HgbA1C patients completed early DM screening versus 83.6% of GTT patients, p< 0.001. Median time to completion was shorter in the HgbA1C group (20 (9,33) vs 25 (13,34) days, p< 0.001). Early diabetes was diagnosed more frequently in the GTT cohort (111/840, 13.2% vs 21/816, 2.6%, p< 0.001). GDM was diagnosed more frequently at 28 week screening in the A1C cohort (154/771, 20.0% vs 106/702, 15.1%, p=0.046) Obstetric and neonatal outcomes including preeclampsia, miscarriage, C-section, preterm birth, macrosomia and shoulder dystocia did not differ between cohorts.

Conclusion:
Using HgbA1C as an initial screen for diabetes in early pregnancy results in higher screening rates and faster completion, but results in lower rates of diagnosis early in pregnancy.