Background: Gestational diabetes mellitus (GDM) is among the most frequently encountered metabolic complications of pregnancy, yet how best to screen for it and when remains a matter of ongoing debate. While the DIPSI glucose challenge test (GCT) is widely recommended in India. There is also a lack of systematic data on how the performance of these tests varies across trimesters, despite clear evidence that insulin resistance increases progressively as pregnancy advances. This gap in evidence  particularly in the context of Indian tertiary care centres  formed the basis for the present study.

Objectives: We undertook this study to directly compare the diagnostic yield of GCT (DIPSI criteria), FBS, and PPBS for GDM detection across all three trimesters of pregnancy, and to examine how each test relates to maternal risk factors and antenatal complications.

Methods: A prospective and retrospective observational study was conducted among 130 pregnant women attending the obstetric OPD at SVS Hospital, Mahbubnagar, between August 2025 and January 2026. All participants underwent FBS, PPBS, and a non-fasting 75g GCT (DIPSI criteria) within their respective trimester. GDM was diagnosed at a 2-hour plasma glucose threshold of ≥140 mg/dL per DIPSI guidelines, with WHO 2013 criteria applied for comparison.

Results: GCT identified GDM in 13.8% of participants, compared to 10.8% detected by FBS and PPBS combined. A combined approach using all three tests yielded the highest detection rate of 16.2%. Mean glucose values rose consistently from the first to the third trimester across all three modalities. GDM prevalence was higher in older women, those with elevated BMI, and grand multipara. Antenatal complications occurred in 36.2% of participants, and GCT showed the strongest correlation with adverse outcomes among all three tests (r=0.63, p<0.01).

Conclusion: GCT outperforms FBS and PPBS as a standalone GDM screening tool and shows the strongest association with adverse antenatal outcomes. A combined screening strategy maximises case detection. Given the progressive rise in GDM prevalence across trimesters, repeat testing at each trimester is essential and should be standard practice. The DIPSI test, requiring no prior fasting, is well suited for routine antenatal care in Indian settings and deserves broader implementation.