Diagnosing gestational diabetes during the Covid-19 pandemic using HbA1c rather than oral glucose tolerance test (OGTT)

ABSTRACT

The Royal College of Obstetrics and Gynaecology advocated replacing OGTT with HbA1c for gestational diabetes (GDM) screening for women with risk factors during the Covid-19 pandemic. HbA1c >=48mmol/mol/random plasma glucose (RPG) >=11.1mmol/l at booking indicated diabetes, and 41-47mmol/ mol/9-11mmol/ l prediabetes or possible GDM. Testing was repeated at 26 weeks if normal previously, with HbA1c >=39mmol/mol, fasting PG >=5.6mmol/l, or RPG >=9mmol/l diagnostic for GDM. A) At her clinic booking visit at 10 weeks gestation, 36 year-old South Asian female had HbA1c 55mmol/mol/RPG 9.5mmol/l suggesting undiagnosed type 2 diabetes. Initially managed with dietary advice and home blood glucose monitoring, metformin was added when self-monitored glucose above pregnancy targets (fasting and pre-meal <5.3mmol/l or 1 h post meal <7.8mmol/l) but insulin was required later. Metformin and insulin were stopped after delivery at 38 weeks with HbA1c 50mmol/mol three months postpartum, supporting the earlier diagnosis of type 2 diabetes. B) 32 year-old White Caucasian female was screened for GDM on booking at 11 weeks as BMI 38 kg/m2. HbA1c 44mmol/mol and RPG 6.9mmol/l confirmed GDM which was managed by dietary/lifestyle changes with glucose and pregnancy targets achieved until 28 weeks when metformin added. Normal delivery at 40 weeks with HbA1c 40mmol/mol three months postpartum triggered advice on long-term dietary/lifestyle changes and annual HbA1c checks. HbA1c was useful during the pandemic but most centres reverted to OGTT for GDM screening due to a significant fall in diagnoses using HbA1c >=39mmol/mol at 26 weeks. But, HbA1c testing was advantageous at booking to diagnose type 2 diabetes earlier.