Glucose tolerance test with a single abnormal value in pregnancy and the risk of type-2 diabetes mellitus

Purpose: To evaluate the association between a single abnormal value on a 3-h 100 g oral glucose tolerance test (OGTT) results and future type-2 diabetes mellitus (Type-2 DM). Methods: Retrospective cohort study of women between 18 and 45 years of age who underwent a 3-h OGTT during pregnancy and delivered in a tertiary medical center between 2007 and 2014. The women were followed for a median period of 64 months postpartum. According to OGTT values, women were divided into three groups: normoglycemic (normal OGTT), single abnormal OGTT value (SAV) and gestational diabetes mellitus (two or more abnormal OGTT values, GDM). General pre-pregnancy characteristics, cardiovascular risk factors and future diagnosis of Type-2 DM, as the primary outcome, were recorded. Results: During the study period, 5295 women underwent an OGTT and were followed for a median period of 64 months (interquartile range of 32). The cohort was divided as following: 3639 (68.73%) were normoglycemic, 854 (16.13%) had a SAV in the OGTT and 802 (15.15%) were diagnosed with GDM. Compared with normoglycemic controls, women with SAV and GDM tended to be older (32.20, 33.10 and 31.35 years for SAV, GDM and controls, respectively, p < 0.001); with higher rates of pre-pregnancy obesity (18.62%, 20.77% and 13.22% for SAV, GDM and controls, respectively, p < 0.001), pre-pregnancy hyperlipidemia (13.35%, 15.30% and 10.52% for SAV, GDM and controls, respectively, p = 0.021) and pre-pregnancy chronic hypertension (5.50%, 4.43% and 3.18% for SAV, GDM and controls, respectively, p = 0.01). Post-pregnancy Type-2 DM was diagnosed at a higher rate among women with SAV or GDM (2.69% for SAV, 7.39% for GDM and 0.66% for normoglycemic controls, p < 0.001). Using a cox proportional hazard regression, SAV and GDM were significantly and independently associated with a higher rate of future overt type-2 diabetes (adjusted aOR 3.59 for SAV and 11.38 for GDM, p < 0.001). In a sub-analysis of the OGTT values, overall, abnormal fasting glucose had the highest correlation with developing future Type-2 DM (8.95% compared with 6.02% for OGTT_60, 6.03% for OGTT_120 and 7.35% for OGTT_180, p < 0.001). A predictive model, combining multiple risk factors, as pre-pregnancy obesity and hypertension with SAV complicating the index pregnancy showed a risk as high as 3.40% for developing future Type-2 DM. Conclusion: SAV is independently associated with a significant higher rate of future Type-2 DM, as early as 5 years following the index pregnancy.