Summary ■Metformin is recommended as first‐line therapy for type 2 diabetes because of its safety, low cost and potential cardiovascular benefits. ■The use of metformin was previously restricted in people with chronic kidney disease (CKD) — a condition that commonly coexists with diabetes — due to concerns over drug accumulation and metformin‐associated lactic acidosis. ■There are limited data from observational studies and small randomised controlled trials to suggest that metformin, independent of its antihyperglycaemic effects, may be associated with lower risk of myocardial infarction, stroke and all‐cause mortality in people with type 2 diabetes and CKD. ■Research into the risk of metformin‐associated lactic acidosis in CKD has previously been limited and conflicting, resulting in significant variation across international guidelines on the safe prescribing and dosing of metformin at different stages of renal impairment. ■Present‐day large scale cohort studies now provide supporting evidence for the safe use of metformin in mild to moderate renal impairment (estimated glomerular filtration rate [eGFR] 30–60 mL/min/1.73m2). However, prescribing metformin in people with severe renal impairment (eGFR < 30 mL/min/1.73m2) remains a controversial issue. Due to observed increased risk of lactic acidosis and all‐cause mortality in people with type 2 diabetes and severe renal impairment, it is generally recommended that metformin is discontinued if renal function falls below this level or during acute renal deterioration.

Background Understanding the risk factors and pregnancy outcomes in women affected by Type 1 and Type 2 diabetes is important for pre‐pregnancy counselling. Aim To explore differences in pregnancy outcomes between women with Type 1 and Type 2 diabetes, and healthy controls, and to examine the relationships between potential adverse risk factors and pregnancy outcomes in this cohort of women. Methods This is a 10‐year retrospective study of women with Type 1 diabetes (n = 92), Type 2 diabetes (n = 106) and healthy women without diabetes (controls) (n = 119) from a tertiary obstetric centre. Clinical and biochemical characteristics of women with Type 1 and Type 2 diabetes were determined and related to major obstetric outcomes using univariate analysis. Results Women with pre‐existing diabetes had higher adverse pregnancy outcomes (preeclampsia, emergency caesarean section, preterm birth <32 and 37 weeks, large for gestational age, neonatal jaundice, Apgar score < 7 at 5 min, neonatal intensive care admission and neonatal hypoglycaemia) compared to controls. A higher birth weight gestational centile (97.4% vs 72.4%, P = 0.001) and large for gestational age rate (63.4% vs 35.8%, P = 0.001) were observed in Type 1 diabetes compared to Type 2 diabetes. There were no differences in other outcomes between women with Type 1 and 2 diabetes. Conclusion In this exploratory study, risk factors for maternal adverse outcomes differ between Type 1 and Type 2 diabetes. Maternal and foetal adverse outcomes were higher in pregnancies affected by diabetes compared to healthy women but occurred with similar frequency in women with Type 1 and Type 2 diabetes.

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