BACKGROUND: Self-monitoring of blood glucose is recommended as a key component of the management plan for diabetes therapy during pregnancy. No existing systematic reviews consider the benefits/effectiveness of various techniques of blood glucose monitoring on maternal and infant outcomes among pregnant women with pre-existing diabetes. The effectiveness of the various monitoring techniques is unclear. OBJECTIVES: To compare techniques of blood glucose monitoring and their impact on maternal and infant outcomes among pregnant women with pre-existing diabetes. SEARCH METHODS: We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (6 August 2013), searched reference lists of retrieved studies and contacted trial authors. SELECTION CRITERIA: Randomised controlled trials (RCTs) comparing techniques of blood glucose monitoring including self blood glucose monitoring, continuous glucose monitoring (CGM) or clinic monitoring among pregnant women with pre-existing diabetes mellitus (Type 1 or Type 2). Trials investigating timing and frequency of monitoring were also included. Quasi-RCTs and RCTs using a cluster-randomised design were eligible for inclusion but none were identified. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed study eligibility, extracted data and assessed the risk of bias of included studies. Data were checked for accuracy. MAIN RESULTS: The search of the Pregnancy and Childbirth Group's Trials Register identified 21 trial reports. Following application of eligibility criteria, nine trials were included in this review. The included trials involved a total of 506 women (436 women with Type 1 diabetes and 70 women with Type 2 diabetes). All trials originated from European countries and the USA. None of the studies included women with gestational diabetes. Five of the nine included studies were at moderate risk of bias and four studies were at low to moderate risk of bias. Primary outcomes were maternal glycaemic control (fasting blood glucose and HbA1c) and infant birthweight or macrosomia.Various methods of glucose monitoring were compared in the trials. The following comparisons were included in the review: (1) self-monitoring versus standard care, (2) self-monitoring versus hospitalisation, (3) pre-prandial versus post-prandial glucose monitoring, (4) automated telemedicine monitoring versus conventional system, (5) CGM versus intermittent monitoring and (6) constant CGM versus intermittent CGM.Neither pooled analyses nor individual trial analyses showed any significant advantages of one monitoring technique over another for primary outcomes (maternal glycaemic control and infant birthweight) and secondary outcomes such as gestational age at birth or preterm birth, frequency of neonatal hypoglycaemia, death of baby including stillbirth, and neonatal intensive care admission. Primary outcome data on macrosomia were reported by one trial but at a different cut-off value than that pre-specified for the review. Secondary outcomes such as shoulder dystocia, major and minor anomalies were not reported by any of the trials. AUTHORS' CONCLUSIONS: This review found no evidence that any glucose monitoring technique is superior to any other technique among pregnant women with pre-existing Type 1 or Type 2 diabetes. The evidence base for the effectiveness of monitoring techniques is weak and additional evidence from large well-designed randomised trials is required to inform choices of glucose monitoring techniques.