Developing twin‐specific 75‐g oral glucose tolerance test diagnostic thresholds for gestational diabetes based on the risk of future maternal diabetes: a population‐based cohort study

Objective To develop twin‐specific outcome‐based oral glucose tolerance test (OGTT) diagnostic thresholds for GDM based on the risk of future maternal type‐2 diabetes. Design A population‐based retrospective cohort study (2007–2017). Setting Ontario, Canada. Methods Nulliparous women with a live singleton ( n = 55 361) or twin ( n = 1308) birth who underwent testing for gestational diabetes mellitus (GDM) using a 75‐g OGTT in Ontario, Canada (2007–2017). We identified the 75‐g OGTT thresholds in twin pregnancies that were associated with similar incidence rates of future type‐2 diabetes to those associated with the standard OGTT thresholds in singleton pregnancies. Results For any given 75‐g OGTT value, the incidence rate of future maternal type‐2 diabetes was lower for women with a twin than women with a singleton pregnancy. Using women with a negative OGTT as reference, the risk of future maternal type‐2 diabetes in twin pregnancies with a positive OGTT based on the standard OGTT thresholds (9.86 per 1000 person years, adjusted hazard ratio (aHR) 4.79, 95% CI 2.69–8.51) was lower than for singleton pregnancies with a positive OGTT (18.74 per 1000 person years, aHR 8.22, 95% CI 7.38–9.16). The twin‐specific OGTT fasting, 1‐hour and 2‐hour thresholds identified in the current study based on correlation with future maternal type‐2 diabetes were 5.8 mmol/l (104 mg/dl), 11.8 mmol/l (213 mg/dl) and 10.4 mmol/l (187 mg/dl), respectively. Conclusions We identified potential twin‐specific OGTT thresholds for GDM that are associated with a similar risk of future type‐2 diabetes to that observed in women diagnosed with GDM in singleton pregnancies based on standard OGTT thresholds. Tweetable abstract Potential twin‐specific OGTT thresholds for GDM were identified.