BACKGROUND: 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.
OBJECTIVES: To assess the effects of different intensities of glycaemic control in pregnant women with pre-existing type 1 or type 2 diabetes.
SEARCH STRATEGY: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (7 May 2010).
SELECTION CRITERIA: We included randomised controlled trials comparing different glycaemic control targets in pregnant women with pre-existing diabetes.
DATA COLLECTION AND ANALYSIS: Two review authors assessed trial eligibility and risk of bias, and extracted data.
MAIN RESULTS: We included three trials all in women with type 1 diabetes (223 women and babies), and all with a high risk of bias. Two trials compared very tight (3.33 to 5.0 mmol/L fasting blood glucose (FBG)) with tight-moderate (4.45 to 6.38) glycaemic control targets, with one trial of 22 babies reporting no perinatal deaths or serious perinatal morbidity. In the same trial, there were two birth defects in the very tight and none in the tight-moderate group with no significant differences in caesarean section between groups (risk ratio 0.92, 95% confidence interval (CI) 0.49 to 1.73). 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); and loose (6.7 to 8.9) glycaemic control targets, there were two neonatal deaths in the loose and none in the tight or moderate groups. There were significantly fewer women with pre-eclampsia, fewer caesareans and fewer birthweights greater than 90th centile in the combined tight-moderate compared with the loose group. AUTHORS' CONCLUSIONS: 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 particularly for pregnant women with type 2 diabetes.