Prevalence and Risk Factors of Gestational Diabetes Mellitus Among Pregnant Women With Normal Body Mass Index At Booking

Abstract

Background: Gestational diabetes mellitus (GDM) is a state of glucose intolerance first recognised during pregnancy. Although high body mass index (BMI) is widely regarded as the primary risk factor, a clinically significant proportion of women who develop GDM fall within the normal BMI range (18.5–24.9 kg/m²). The prevalence and specific risk determinants in this subgroup remain inadequately characterised, particularly in the South Indian context.

Objectives: To determine the prevalence of GDM among pregnant women with normal BMI at booking, to compare sociodemographic, obstetric, and biochemical characteristics between GDM and non-GDM women in this cohort, and to identify independent risk factors for GDM development in this subgroup.

Methods: A retrospective cohort study of 350 pregnant women with normal BMI at booking, attending a tertiary care hospital in Tamil Nadu (January–December 2024). Universal GDM screening was conducted using the DIPSI (Diabetes in Pregnancy Study Group India) non-fasting 75g oral glucose challenge test at three timepoints: 8–12 weeks, 24–28 weeks (if 1st was negative), and 32–34 weeks (if both prior screens were negative). A DIPSI result ≥140 mg/dL constituted a positive screen; thereafter, the DIPSI test was not repeated. Instead, fasting blood sugar (FBS) and 2-hour postprandial blood sugar (2hr PPBS) were used for glycaemic characterisation and fortnightly monitoring.

Results: The prevalence of GDM in this normal-BMI cohort was 10.3% (36/350; 95% CI: 7.3–13.9%). Mean age in the GDM group was significantly higher (29.2±4.6 vs. 25.8±4.1 years, p<0.001). Independent risk factors on multivariable analysis were: age ≥30 years (aOR 2.9, 95% CI: 1.4–5.8), family history of T2DM (aOR 3.6, 95% CI: 1.8–7.2), previous GDM (aOR 5.4, 95% CI: 2.0–14.5), BMI 23–24.9 kg/m² (aOR 2.2, 95% CI: 1.1–4.4), and elevated booking FPG 86–92 mg/dL (aOR 2.5, 95% CI: 1.2–5.1).

Conclusion: GDM prevalence in normal-BMI South Indian women is substantial (10.3%). Universal DIPSI-based screening with structured FBS/PPBS monitoring is essential and should not be deferred on the basis of normal BMI alone. Targeted risk stratification by age, family history, and early-pregnancy glycaemic markers can optimise detection.