Prevalence of gestational diabetes mellitus and the effect of weight on measures of insulin secretion and insulin resistance in third-trimester pregnant rural women residing in the Central Region of Limpopo Province, South Africa

Aim: To examine the prevalence of gestational diabetes in third-trimester pregnant women as well as to assess their insulin secretion and insulin resistance (IR). Methods: Third-trimester pregnant women (n = 262) attending antenatal care at local clinics in the central region of the Limpopo Province underwent a 2-h oral glucose tolerance test (OGTT) with blood collected at 0, 30 and 120 min. Glucose and insulin were measured. Results: The prevalence of gestational impaired glucose tolerance (GIGT) and gestational diabetes mellitus (GDM) was 8.8% (7.3% GIGT; 1.5% GDM). Women with GIGT/GDM were significantly older and had more children compared with women with a normal response to the OGTT. Homeostasis model assessment (HOMA)-IR and fasting insulin were lower in the GIGT/GDM group compared with the normal group, as were measures of insulin secretion (HOMA B-cell function and insulinogenic index). Furthermore, women with body mass index (BMI) >= 30.0 kg/m(2) were significantly older and had higher parity, systolic and diastolic blood pressure measurements than those with BMI 25.0-29.9 kg/m(2) and BMI < 25.0 kg/m(2). However, increased BMI was not associated with an increased risk of GIGT/GDM. Conclusions: The present study shows that there is a high prevalence of GIGT/GDM, with most women having IGT. The GIGT/GDM present in these women is characterized by increased insulin sensitivity accompanied by reduced pancreatic B-cell function. Additionally, heavier women appear to have increased first phase insulin secretion, suggesting the presence of insulin resistance.