179-LB: Should We Screen with a Fasting Blood Glucose Test? A Novel Two-Step Screening Strategy for Gestational Diabetes—A Large Tertiary Comparative Cohort Study

Background: Gestational diabetes mellitus (GDM) diagnosis is resource intensive and controversial. A modified COVID-19 GDM diagnostic method was introduced at Western Health Melbourne, an Australian tertiary hospital caring for a multi-ethnic population with a high GDM prevalence at 20-23%. In place of a universal 2 hour 75g OGTT, a novel two step diagnostic method was instituted. A fasting blood glucose (FBG) was performed with thresholds based on a secondary analysis of HAPO data. A FBG of ≥5.1mmol/L (91.8mg/dL) diagnosed GDM; women with FBG 4.7-5.0mmol/L (84.6-90.0mg/dL) proceeded to an OGTT (IADPSG diagnostic criteria); FBG ≤4.6mmol/L (82.8mg/dL) was considered to exclude GDM.

Methods: A retrospective cohort study of singleton pregnancies birthing after 20 weeks’ gestation compared perinatal outcomes in 6469 women who underwent modified screening (MS) during the COVID-19 pandemic with 8669 women who had conventional screening (CS) prior to COVID-19.

Results: GDM prevalence was the same using either MS or CS (22.9 vs 22.2% p=0.31) with similar rates of insulin use. There was no difference in the prevalence of large for gestational age infants (10.3 vs 9.4% p=0.06), pre-term birth (6.6 vs 6.4% p=0.53) or gestational age at birth (39.2 vs 39.1 weeks). Mean birth weight was increased with MS (3335g vs 3307g) and small for gestational age rate reduced (9.1 vs 10.5% p=0.01). The MS group had fewer inductions (34.2 vs 39.8% p<0.01). Primary caesarean section rate was unchanged (18.4 vs 18.4% p=0.91). MS reduced the need for an OGTT by 76%. Women with a FBG ≤4.6mmol/L by MS had non-inferior outcomes compared to women with a FBG ≤4.6mmol/L with CS irrespective of GDM diagnosis.

Conclusion: In a large multi-ethnic cohort with a high prevalence of GDM, modified screening using FBG greatly reduced the number of resource intensive OGTTs with non-inferior perinatal outcomes. A prospective randomised trial comparing these methods is warranted.