Our study analyzed the long-term T2D risk among women with prior GDM or IGT, aligning with the outcomes of the Diabetes Prevention Program.2 The study highlights the critical need for early, specific post-GDM interventions to curb T2D progression. Over 25 years, risk trajectories for T2D notably diverged between the cohorts, with particular variance in some demographics. Women aged over 35 years, of Māori ethnicity, or facing socioeconomic challenges in the GDM cohort showed increased T2D risk compared with their IGT counterparts. This aligns with prior studies emphasizing the elevated T2D risk post-GDM in specific populations, advocating for focused interventions.10 11 While previous studies have shown a uniformly elevated risk of T2D across all age groups post-GDM,5 our results indicate that this elevated risk is more pronounced in older women, particularly those over 35 years. This discrepancy suggests that age-specific factors may play a more significant role in T2D progression than previously thought.

Our research highlights the significant impact of socioeconomic status on T2D risk, echoing findings of the heavier toll from diabetes on impoverished communities.12 Integrating social health determinants into diabetes prevention is essential, aligning with the WHO’s initiative against non-communicable disease inequities.13 Although our study found that socioeconomic deprivation was a more potent predictor of T2D risk among women with prior GDM compared with those with IGT, this contrasts with some studies suggesting an equal impact across different glucose intolerant conditions.14 While the current study used integrated socioeconomic status measurements, as opposed to the single social determinants employed in previous studies, further research with similar design and socioeconomic status metrics is warranted. The increased risk in the GDM cohort within the first 5 years post partum indicates a critical period for intervention as reported elsewhere.15 This time frame is ideal for implementing lifestyle and pharmacological measures to prevent T2D progression, supporting guidelines that recommend early postpartum glucose assessments.16 Early intervention can address modifiable risk factors effectively during this window, potentially altering the disease trajectory.

The association between renal function, as indicated by eGFR rates, and T2D risk in our study resonates with a growing body of evidence linking early renal function decline with future T2D risk.17 18 This calls for renal function to be a focal point in the post-GDM follow-up, especially considering the potential for intervention at stages of renal impairment that precede overt kidney disease. This calls for integrating renal function monitoring into routine postpartum care for women with GDM, which could mitigate long-term renal and metabolic complications.

Traditional risk models have linked smoking to T2D.19 Our study revealed inconsistency in T2D risk between GDM and IGT cohorts based on smoking status. Among non-smokers, the HR for T2D was significant, indicating a higher risk in the GDM cohort compared with the IGT cohort. However, among current or ex-smokers, the HR was not significant, suggesting no difference in T2D risk between the cohorts. This suggests GDM screening identifies at-risk individuals lacking conventional risk factors. In contrast, the IGT cohort may identify those with metabolic syndrome reflecting the indication for the OGTT. However, due to the small sample size of the smoking subgroup, further research with larger sample sizes is needed to confirm this finding. Ethnic disparities in diagnosis rate, particularly among Pasifika and Māori, might reflect differences in screening practices, with Māori possibly receiving more comprehensive T2D screening. A noted low retinopathy prevalence in newly diagnosed Māori diabetics suggests effective screening in certain areas.20 These paradoxes highlight T2D risk factors’ complexity, urging further study into post-GDM lifestyle changes and screening practice disparities’ impact on long-term outcomes.

The slightly higher BMI and blood pressure in the IGT cohort reveal a subtle dynamic; these elevations, though not statistically linked to increased T2D risk, suggest metabolic syndrome’s presence without clear risk factors.21 This highlights the role of GDM screening in pinpointing T2D risk among women lacking traditional indicators. It advocates for a comprehensive clinical approach, emphasizing the importance of assessing metabolic syndrome in women post-GDM. A holistic strategy incorporating weight and blood pressure management is essential for preventing T2D, underscoring the necessity of focused interventions for this group. Such measures are in line with studies showing that managing metabolic syndrome elements can notably lower T2D risk.22

Our study has some limitations. The analysis was retrospective and observational, which precludes causal inferences. Additionally, the generalizability of our findings may be constrained by the distinct ethnic and socioeconomic composition of the cohort, the NZ setting, and the employment of the NZSSD criteria. This specific ethnic mix and criterion application might not fully translate to other populations or contexts, suggesting a need for cautious application of the study conclusions beyond NZ. The lack of statistical significance in the overall HR suggests that while a trend toward higher risk in the GDM group was observed, it does not definitively confirm a greater T2D risk. This limitation should be considered when interpreting subgroup analyses, which may reflect variability in risk factors rather than consistent, significant differences. Many subgroup analyses also yielded insignificant estimations, highlighting the variability and lack of definitive evidence for some observed differences in T2D risk. These wide CIs may be due to sample size limitations within subgroups, particularly among smokers and ethnic minorities. Additionally, the potential effects of unmeasured confounders, variability in clinical management, and differing health-seeking behaviors between groups may have contributed to the non-significant findings. Future studies with larger sample sizes and more comprehensive measurements (eg, physical activity and nutrition exposures) are needed to explore these relationships more thoroughly.

In the current study, our primary objective was to compare the long-term risk of developing type 2 diabetes mellitus (T2DM) between women with GDM and those with IGT. Future research should consider including a subgroup of women who developed T2DM without prior diagnoses of GDM or IGT to allow for more thorough comparisons and to enhance the understanding of different pathways leading to T2DM. This additional analysis could provide valuable insights into the distinct risk profiles and progression patterns among these groups. However, it is important to note that our current study was limited to data on women diagnosed with GDM or IGT, and we did not have access to data for women who developed T2DM without these prior diagnoses.