Philippa Middleton, Caroline A Crowther, Lucy Simmonds

The optimal glycaemic control target in pregnant women with pre-existing diabetes is unclear, although there is a clear link between high glucose concentrations and adverse birth outcomes. To assess the effects of different intensities of glycaemic control in pregnant women with pre-existing type 1 or type 2 diabetes. We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (31 January 2016) and planned to search reference lists of retrieved studies. We included randomised controlled trials comparing different glycaemic control targets in pregnant women with pre-existing diabetes. Two review authors independently assessed trials for inclusion, conducted data extraction, assessed risk of bias and checked for accuracy. We assessed the quality of the evidence using the GRADE approach. We included three trials, all in women with type 1 diabetes (223 women and babies). All three trials were at high risk of bias due to lack of blinding, unclear methods of randomisation and selective reporting of outcomes. Two trials compared very tight (3.33 to 5.0 mmol/L fasting blood glucose (FBG)) with tight-moderate (4.45 to 6.38 mmol/L) glycaemic control targets, with one trial of 22 babies reporting no perinatal deaths orserious perinatal morbidity (evidence graded low for both outcomes). In the same trial, there were two congenital anomalies in the very tight, and none in the tight-moderate group, with no significant differences in caesarean section between groups (risk ratio (RR) 0.92, 95% confidence interval (CI) 0.49 to 1.73; evidence graded very low). In these two trials, glycaemic control was not significantly different between the very tight and tight-moderate groups by the third trimester, although one trial of 22 women found significantly less maternal hypoglycaemia in the tight-moderate group.In a trial of 60 women and babies comparing tight (≤ 5.6 mmol/L FBG); moderate (5.6 to 6.7 mmol/L); and loose (6.7 to 8.9 mmol/L) glycaemic control targets, there were two neonatal deaths in the loose and none in the tight or moderate groups (evidence graded very low). There were significantly fewer women with pre-eclampsia (evidence graded low), fewer caesarean sections (evidence graded low) and fewer babies with birthweights greater than 90th centile (evidence graded low) in the combined tight-moderate compared with the loose group.The quality of the evidence was graded low or very low for important outcomes, because of design limitations to the studies, the small numbers of women included, and wide confidence intervals crossing the line of no effect. Many of the important outcomes were not reported in these studies. In a very limited body of evidence, few differences in outcomes were seen between very tight and tight-moderate glycaemic control targets in pregnant women with pre-existing type 1 diabetes, including actual glycaemic control achieved. There is evidence of harm (increased pre-eclampsia, caesareans and birthweights greater than 90th centile) for 'loose' control (FBG above 7 mmol/L). Future trials comparing interventions, rather than glycaemic control targets, may be more feasible. Trials in pregnant women with pre-existing type 2 diabetes are required.