Interventions to prevent women from developing gestational diabetes mellitus: an overview of Cochrane Reviews

Background The prevalence of gestational diabetes mellitus (GDM) is increasing, with approximately 15% of pregnant women affected worldwide, varying by country, ethnicity and diagnostic thresholds. There are associated short‐ and long‐term health risks for women and their babies. Objectives We aimed to summarise the evidence from Cochrane systematic reviews on the effects of interventions for preventing GDM. Methods We searched the Cochrane Database of Systematic Reviews (6 August 2019) with key words ‘gestational diabetes’ OR ’GDM’ to identify reviews pre‐specifying GDM as an outcome. We included reviews of interventions in women who were pregnant or planning a pregnancy, irrespective of their GDM risk status. Two overview authors independently assessed eligibility, extracted data and assessed quality of evidence using ROBIS and GRADE tools. We assigned interventions to categories with graphic icons to classify the effectiveness of interventions as: clear evidence of benefit or harm (GRADE moderate‐ or high‐quality evidence with a confidence interval (CI) that did not cross the line of no effect); clear evidence of no effect or equivalence (GRADE moderate‐ or high‐quality evidence with a narrow CI crossing the line of no effect); possible benefit or harm (low‐quality evidence with a CI that did not cross the line of no effect or GRADE moderate‐ or high‐quality evidence with a wide CI); or unknown benefit or harm (GRADE low‐quality evidence with a wide CI or very low‐quality evidence). Main results We included 11 Cochrane Reviews (71 trials, 23,154 women) with data on GDM. Nine additional reviews pre‐specified GDM as an outcome, but did not identify GDM data in included trials. Ten of the 11 reviews were judged to be at low risk of bias and one review at unclear risk of bias. Interventions assessed included diet, exercise, a combination of diet and exercise, dietary supplements, pharmaceuticals, and management of other health problems in pregnancy. The quality of evidence ranged from high to very low. Diet Unknown benefit or harm: there was unknown benefit or harm of dietary advice versus standard care, on the risk of GDM: risk ratio (RR) 0.60, 95% CI 0.35 to 1.04; 5 trials; 1279 women; very low‐quality evidence. There was unknown benefit or harm of a low glycaemic index diet versus a moderate‐high glycaemic index diet on the risk of GDM: RR 0.91, 95% CI 0.63 to 1.31; 4 trials; 912 women; low‐quality evidence. Exercise Unknown benefit or harm: there was un