Diabetes mellitus is the term used for a group of heterogeneous disorders characterised by glucose intolerance and hyperglycaemia resulting either from excess glucose or the lack of effect of endogenous insulin. This metabolic condition results in changes in many aspects of bodily haemostasis but also has an effect on reproductive capability from conception, to pregnancy and childbirth. This chapter describes the pathophysiology of type 1, insulin-dependent diabetes mellitus, its treatment and control, the relevant aspects for fertility, pregnancy and management of gestational diabetes. There is further discussion of the relationship between type 2, non-insulin-dependent diabetes, insulin resistance, hyperinsulinaemia and PCOS (see also Chapter 9).

Banting and Best first described insulin in 1922. This revolutionised the management of type 1 diabetes, which had severe implications for pregnant women and their children. The perinatal mortality in diabetic pregnancy was at that time 440/1000 and it continued at that level for several decades until improvements in prepregnancy and antepartum control were made. Maternal and fetal morbidity and mortality have been greatly improved through the combined effects of a greater understanding of the disease, the use of more purified insulins with variable duration of effect and improved surveillance during pregnancy. In recognition of the variable but still excessive morbidity and mortality, the St Vincent declaration of 1989 set a five-year target for reduction of adverse pregnancy outcomes among women with type 1 diabetes to a level equivalent to that among women without diabites.