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The International Diabetes Federation (IDF) reports that 1 in 6 (16.8%) pregnancies are affected by diabetes [13]. Of this number, 13.6% are affected by pregestational diabetes, while the majority (86.4%) are affected by GDM. While it might be expected that rates of pregestational diabetes would reflect background diabetes prevalence in the general population [31], a population-based cohort study in Sweden revealed reduced fertility among women with diabetes [32]. Overall, the fertility among women with type 1 diabetes recorded between 1965 and 2004 was reduced by 20%, with the presence of microvascular or cardiovascular complications associated with particularly low fertility. Although the presence of complications was associated with subfertility throughout all calendar-year strata, the reduced fertility was confined to women first hospitalized before 1985. This suggests that improved diabetes management such as tighter glycemic control may help to eliminate this phenomenon moving forward. Fertility rates among women with type 2 diabetes (or indeed other types of pregestational diabetes) are not described, but they would be expected to be lower than average considering the associated obesity and polycystic ovarian syndrome [31].

Albrecht et al. [33] examined national hospital discharge data in the United States from 1994 to 2004. They found that women with type 1 diabetes, type 2 diabetes, and unspecified diabetes accounted for 7.0, 4.0, and 3.6% of delivery hospitalizations with diabetes. Interestingly, while rates of all types of diabetes significantly increased overall, the largest percent increase for all ages was in type 2 diabetes (367%) [33]. This is in keeping with the worldwide epidemic of type 2 diabetes, something that has developed over the past 50 years and continues to grow [31]. This epidemic is fuelled by obesity; and of significant future concern is the increasing numbers of overweight and obese women becoming pregnant [34], along with a parallel rise in body mass index (BMI) among children and adolescents [35]. Indeed, additional work by Correa et al. [36] corroborates the increasing trends of pregestational diabetes in the United States, indicating that they continued through to 2009. In 2009, the overall prevalence of pregestational diabetes increased monotonically with maternal age and was higher among women with public versus private insurance (OR 1.29) and in patients who resided in postal locations where the median household income was in the lowest quartile (OR 1.54) [36]. The dramatic increase in type 2 diabetes is further highlighted by more recent data from the fourth National Pregnancy in Diabetes Audit in the UK, which reports on 3,297 women with pregestational diabetes [37]. The audit report reveals that for the first time, half of included women with pregestational diabetes had a diagnosis of type 2 diabetes. These women are typically older, have a much shorter duration of diabetes, a higher BMI than women with type 1 diabetes with over 40% representing the most deprived socioeconomic group, and 50% were of Asian, Black, or Mixed Race.

As eluded to previously, the baseline clinical characteristics of pregnant women with pregestational diabetes have changed over time. This has been clearly demonstrated by Danish researchers in the case of nephropathy in type 1 diabetes where the prevalence has declined from 5% in the late 1990s to 2.5% between 2007 and 2012 [38, 39]. It may be postulated that this decline is due to improved glycemic control and more frequent use of inhibitors of the renin–angiotensin system. Interestingly, these researchers noted that the prevalence of kidney involvement was comparable in women with type 1 and those with type 2 diabetes, the latter group having a much shorter duration of disease on average. This reflects observations in the nonpregnant population of young adults with type 2 diabetes where microalbuminuria and diabetic nephropathy appear to complicate diabetes at an earlier stage in the disease course [40]. While approximately two-thirds of women with type 1 diabetes have documented retinopathy during pregnancy, sight-threatening disease is relatively rare, again likely reflecting improved treatment modalities [41, 42].

There are limited data on distribution of other specific types of diabetes in pregnancy. Using data from a cohort of patients from the population-based Atlantic Diabetes in Pregnancy study along the Irish Atlantic seaboard, a prevalence of 1.1 in 1,000 was calculated for glucokinase monogenic diabetes [43]. Combined criteria of BMI <25 kg/m² and fasting glucose ≥5.5 mmol/L were found to have a sensitivity of 68% and specificity of 96% for the condition. With increasing life expectancy, more women with cystic fibrosis and diabetes mellitus become pregnant [44]. Although precise prevalence estimates are unavailable, pregnancies affected by cystic fibrosis have become increasingly common since 1990 [45].

Table 2. Classical maternal risk factors for GDM