Insulin secretory defect may be the major determinant of GDM in lean mothers.

Aims: To compare the insulin sensitivity and secretion indices of pregnant Bangladeshi women with GDM and normal glucose tolerance (NGT).

Methods: This cross sectional study was performed with 40 GDM and equal number of NGT pregnant women diagnosed on basis of WHO criterion-2013 during 24-40 weeks of gestation. Glucose was measured by glucose oxidase method and fasting insulin by chemiluminescent immunoassay. Equations of homeostatic model assessment (HOMA) were used to calculate indices of insulin resistance (HOMA-IR), β-cell function (HOMA-B) and insulin sensitivity (HOMA-%S).

Results: The GDM group had significantly higher insulin resistance as indicated by higher fasting insulin value [GDM vs. NGT; 10.23 (7.94-14.50) vs. 7.07 (5.28-11.07) µIU/ml] and HOMA-IR [GDM vs. NGT; 2.47 (1.75-3.43) vs. 1.50 (0.99-2.22)] and poor β-cell secretion [GDM vs. NGT; HOMA-B: 113.37 (90.30-191.35) vs. 150.98 (109.85-271.72), median (IQR); p < 0.001 for all]. HOMA-B was significantly lower in GDM than NGT with BMI < 23 kg/m [GDM vs. NGT; 63.37 (49.19-83.83) vs. 134.89 (93.50-193.17) ng/ml; p = 0.010] despite having statistically comparable difference in IR. BMI was found to be a significant predictor of HOMA-IR in GDM.

Conclusions: Though impairments of both insulin secretion and sensitivity are hallmarks in the pathogenesis of GDM, β-cell dysfunction contributes more to development of GDM in those with relatively lower BMI in our population.