Estimated treatment effects of tight glycaemic targets in mild gestational diabetes mellitus: a multiple cut-off regression discontinuity study design.

Abstract Background We investigated the treatment effects of tight glycaemic targets in a population universally screened according to the International Association of Diabetes and Pregnant Study Groups/World Health Organisation gestational diabetes mellitus (GDM) guidelines. Methods A multiple cut-off regression discontinuity study design in a retrospective observational cohort undergoing oral glucose tolerance tests (n = 1178). Treatment of GDM women with the targets: fasting glucose of ≤ 5.0 mmol/L and the 2-hour post-prandial glucose of ≤ 6.7 mmol/L. Results Treated GDM women had lower rates of large for gestational age 4.6% versus those just below diagnostic thresholds 12.6%, relative risk 0.37 (95% CI, 0.16–0.85); reduced caesarean section rates, 32.2% versus 43.0%, relative risk 0.75 (95% CI, 0.56–1.01). The subgroup analysis suggested that treatment of GDM women with BMI ≥ 30 kg/m2 drove the reduction in caesarean section rates: 32.9% versus 55.9%, relative risk 0.59 (95%CI, 0.4–0.87). Linear regression interaction term effects between non-GDM and treated GDM were significant for LGA (p = 0.001) and caesarean sections (p = 0.015). Conclusions Tight glycaemic targets reduced rates of large for gestational age and caesarean sections compared to a counterfactual group just below the diagnostic thresholds albeit at the expense of increased rates of neonatal hypoglycaemia, induced deliveries, and insulin usage.