Do raised two-hour pre-pregnancy insulin levels confer the same risks of developing GDM, as raised fasting levels, in recurrent miscarriage patients?

This study questioned whether raised pre-pregnancy two-hour (2 h) insulin levels, measured in recurrent embryonic miscarriage (RM) patients via a 75 g Oral Glucose Tolerance Test (OGTT), are associated with an increased risk of gestational diabetes mellitus (GDM) in a subsequent pregnancy. Patients had a 75 g OGTT and insulin levels evaluated (n = 170). 54.1% had normal glucose and insulin levels, 45.9% had levels indicating hyperinsulinism (HI). In the 98 patients who achieved a pregnancy, the prevalence of GDM was 3.7% in those without HI, and 35.7% in the patients who only had raised 2 h insulin levels. While HI has been described as a risk factor for miscarriages only in relation to raised fasting (basal) insulin levels, this study demonstrated that raised 2 h insulin levels predict an increased risk of GDM in a subsequent pregnancy. Thus raised 2 h insulin levels likely confer a similar risk to raised fasting insulin levels in RM patients.Impact statementWhat is already known on this subject? Fasting hyperinsulinism is known to be associated with an increased risk of gestational diabetes mellitus (GDM) in pregnancy. Hyperinsulinism, as reflected by the fasting (basal) insulin levels >20mU/L, has been recognized as a risk factor for recurrent miscarriages, particularly in patients with polycystic ovarian syndrome (PCOS), in the World literature. Raised two-hour insulin levels have not been considered as a risk factor in the literature before.What do the results of the study add? We have demonstrated a 10-fold increase in the development of GDM in patients with fasting insulin resistance, and/or raised 2h insulin levels, and an almost 10-fold increase in patients with only raised 2h levels. 58.8% of the patients who subsequently developed GDM only had raised 2h levels and would have been missed with routine testing.What are the implications of these findings for clinical practice and/or further research? Our study has demonstrated that GDM was three times more prevalent in the patients with only raised 2h levels, than in those only with raised fasting levels, reflecting insulin resistance/hyperinsulinism. Insulin studies including 2h insulin levels are therefore an important factor to consider when working up these patients. Insulin studies pre-pregnancy may be useful in identifying women at risk of suffering miscarriages or of developing GDM in a subsequent pregnancy.