Abstract: This review update includes a total of 12 trials (944) women (type 1 diabetes: 660 women; type 2 diabetes: 113 women; type 1 or type 2 (unspecified): 171 women. The trials took place in Europe, the USA and Canada. Three of the 12 included studies are at low risk of bias, eight studies are at moderate risk of bias, and one study is at high risk of bias. Four trials reported that they were provided with the continuous glucose monitors free of charge or at a reduced cost by the manufacturer. Continuous glucose monitoring (CGM) versus intermittent glucose monitoring, (four studies, 609 women) CGM may reduce hypertensive disorders of pregnancy (pre-eclampsia and pregnancy-induced hypertension) (risk ratio (RR) 0.58, 95% confidence interval (CI) 0.39 to 0.85; 2 studies, 384 women; low-quality evidence), although it should be noted that only two of the four relevant studies reported data for this composite outcome. Conversely, this did not translate into a clear reduction for pre-eclampsia (RR 0.65, 95% CI 0.39 to 1.08; 4 studies, 609 women, moderate-quality evidence). There was also no clear reduction in caesarean section (average RR 0.94, 95% CI 0.75 to 1.18; 3 studies, 427 women; I2 = 41%; moderate-quality evidence) or large-for-gestational age (average RR 0.84, 95% CI 0.57 to 1.26; 3 studies, 421 women; I2 = 70%; low-quality evidence) with CGM. There was not enough evidence to assess perinatal mortality (RR 0.82, 95% CI 0.05 to 12.61, 71 infants, 1 study; low-quality evidence), or mortality or morbidity composite (RR 0.80, 95% CI 0.61 to 1.06; 1 study, 200 women) as the evidence was based on single studies of low quality. CGM appears to reduce neonatal hypoglycaemia (RR 0.66, 95% CI 0.48 to 0.93; 3 studies, 428 infants). Neurosensory disability was not reported. Other methods of glucose monitoring For the following five comparisons, self-monitoring versus a different type of self-monitoring (two studies, 43 women); self-monitoring at home versus hospitalisation (one study, 100 women), pre-prandial versus post-prandial glucose monitoring (one study, 61 women), automated telemedicine monitoring versus conventional system (three studies, 84 women), and constant CGM versus intermittent CGM (one study, 25 women), it is uncertain whether any of the interventions has any impact on any of our GRADE outcomes (hypertensive disorders of pregnancy, caesarean section, large-for-gestational age) because the quality of the evidence was found to be very low. This was due to evidence largely being derived from single trials, with design limitations and limitations with imprecision (wide CIs, small sample sizes, and few events). There was not enough evidence to assess perinatal mortality and neonatal mortality and morbidity composite. Other important outcomes, such as neurosensory disability, were not reported in any of these comparisons. Two new studies (406 women) have been incorporated to one of the comparisons for this update. Although the evidence suggests that CGM in comparison to intermittent glucose monitoring may reduce hypertensive disorders of pregnancy, this did not translate into a clear reduction for pre-eclampsia, and so this result should be viewed with caution. There was no evidence of a difference for other primary outcomes for this comparison. The evidence base for the effectiveness of other monitoring techniques analysed in the other five comparisons is weak and based on mainly single studies with very low-quality evidence. Additional evidence from large well-designed randomised trials is required to inform choices of other glucose monitoring techniques and to confirm the effectiveness of CGM.

Plain-language summary: This is an update of a review first published in 2014, updated in 2017. We searched for evidence from randomised controlled studies in November 2018. We identified 12 studies involving 944 women (type 1 diabetes: 660 women; type 2 diabetes: 113 women; in two trials (171 women) there was a mix of type 1 and type 2 diabetes. The trials were from Europe, USA and Canada. There were six comparisons. These were: continuous versus intermittent monitoring of blood glucose (four studies, 609 women); two different ways of self-monitoring (two studies, 43 women); self-monitoring at home versus hospitalisation to control blood glucose levels (one study, 100 women); blood glucose monitoring before a meal (pre-prandial) versus blood glucose monitoring after a meal (post-prandial) (one study, 61 women); automated telemedicine monitoring versus conventional care (three studies, 84 women); and constant continuous monitoring versus intermittent continuous monitoring (one study, 25 women), Continuous versus intermittent monitoring may reduce overall high blood pressure problems during pregnancy (two studies, 384 women, low-quality evidence). However, it should be noted that only two of four relevant studies reported data for this outcome. There was more evidence on high blood pressure and protein in their urine (pre-eclampsia), which showed no clear difference (four studies, 609 women). We also found no difference in the number of women having a caesarean section (three studies, 427 women; moderate-quality evidence). There was not enough evidence to assess infant deaths or the combined outcome of infant deaths and ill-health as these outcomes were based on single studies. Four studies received some support from commercial partners. The other comparisons of different ways of monitoring blood glucose levels were based on very small studies or single studies with very low-quality evidence that did not show any clear differences in outcomes. Although the evidence from randomised controlled studies suggests that continuous monitoring of blood glucose levels may be more effective in reducing high blood pressure problems during pregnancy, only two studies reported on this. There was no clear reduction for pre-eclampsia based on evidence from four studies. For other methods of glucose monitoring, the review showed that there is not enough evidence to say with any certainty which monitoring method for blood glucose is best. More research is needed to find out which other monitoring method is best at reducing the risk of complications for pregnant women with pre-existing diabetes and to confirm the effectiveness of continuous glucose monitoring.