Despite recent advances in care, women with diabetes in pregnancy are still at increased risk of multiple pregnancy complications. Offspring exposed to hyperglycaemia in utero also experience long-term health sequelae, affecting neurocognitive and cardiometabolic status. Many of these adverse consequences can be prevented or ameliorated with good medical care, specifically to optimize glycaemic control. The accurate assessment of glycaemia in pregnancy is therefore vital to safeguard the health of mother and child. However, there is no consensus about the best method of monitoring glycaemic control in pregnancy. Short-term changes in insulin dosage and lifestyle, with altered appetite, insulin sensitivity and red cell turnover create difficulties in interpretation of standard laboratory measures such as HbA1c. The ideal marker would provide short-term feedback on daily or weekly glycaemic control, with additional capability to predict pregnancies at high risk of suboptimal outcomes. Several novel biochemical markers are available which allow assessment of dynamic changes in glycaemia over weeks rather than months. Continuous glucose monitoring devices have advanced in accuracy and provide new opportunities for robust assessment of glycaemia in pregnancy. Recent work from the continuous glucose monitoring in pregnant women with type 1 diabetes trial (CONCEPTT) has provided information about the ability of different markers of glycaemia to predict pregnancy outcomes.The aim of this review is to summarize the care for women with pre-existing diabetes in pregnancy and to highlight the important role of glycaemic monitoring in pregnancy.