The association of immediate postpartum glucose values with persistent insulin resistance in patients with gestational diabetes

Abstract

Objective: Gestational diabetes (GDM) affects approximately 6% of pregnancies and has critical maternal and neonatal implications.¹ About 20-33% of these patients have insulin resistance or type 2 diabetes when evaluated at 6 to 12 weeks postpartum, however only approximately half of the affected patients return for postpartum testing.^2-5 Fasting glucose during delivery hospitalization is correlated with fasting glucose on oral glucose tolerance testing (OGTT) at 4 to 12 weeks postpartum, but there is limited data on the utility of this value to identify the patients at an increased risk for postpartum insulin resistance.³ We aimed to evaluate if higher fasting glucose values on postpartum day 1 (PPD1) are correlated with an increased risk of persistent insulin resistance at 4 to 12 weeks postpartum diagnosed on OGTT.

Study design: We conducted a retrospective cohort study of patients with GDM who delivered from 2009 to 2019 at 2 suburban hospitals. Eligible patients had a singleton pregnancy affected by GDM with complete data on PPD1 fasting glucose and OGTT at 4 to 12 weeks postpartum. GDM was diagnosed by a 50 gram, 1-hour OGTT value of ≥200 mg/dL or a 3-hour glucose tolerance test with ≥2 values exceeding defined thresholds (Carpenter-Coustan criteria). Postpartum impaired fasting glucose was defined as a fasting glucose ≥100 mg/dL, and impaired glucose tolerance was defined as a 2-hour glucose ≥140 mg/dL on postpartum glucose tolerance testing. PPD1 fasting glucose values were divided into 3 categories (<95, ≥95 to 109, and ≥110 mg/dL) for analyses. Univariate analyses were performed using chi-squared, analysis of variance, and Wilcoxon rank-sum tests as appropriate to evaluate the association between an abnormal postpartum OGTT and demographic variables, clinical characteristics, and PPD1 glucose by glucose category. Logistic regression models were performed to adjust for variables that were determined a priori and those found to be significant (P<.05) in univariate analyses. Sensitivity, specificity, positive predictive value, and negative predictive value were calculated using descriptive statistics.

Results: Our analysis included 367 patients (Figure), of which 69.5% (255/367) had a PPD1 glucose <95 mg/dL, 19.9% (73/367) had a PPD1 glucose of 95 to 109 mg/dL, and 10.6% (39/367) had a PPD1 glucose ≥110 mg/dL. In multivariate analysis, compared with PPD1 <95 mg/dL, there was no significant association between postpartum glucose categories and abnormal postpartum OGTT results (PPD1 glucose ≥95 to 109 mg/dL: aOR [adjusted odds ratio], 1.10; 95% CI [confidence interval], 0.58-2.07; P=.77; PPD1 glucose ≥110 mg/dL: aOR, 1.01; 95% CI, 0.44-2.30; P=.99, Table). Fasting glucose on PPD1 of 95 mg/dL had a sensitivity of 20.1% (95% CI, 13.8-27.8%), specificity of 81.2% (95% CI, 76.4-85.4%), positive predictive value of 32.2% (95% CI, 22.6-43.1%), and negative predictive value of 69.7% (95% CI, 64.7-74.3%) to identify patients with impaired fasting glucose, impaired glucose tolerance, or type 2 diabetes postpartum. In identifying patients with type 2 diabetes at 4 to 12 weeks postpartum, fasting glucose of 95 mg/dL on PPD1 had a sensitivity of 1.79% (95% CI, 0.2-6.3%), specificity of 98.4% (95% CI, 96.0-99.6%), positive predictive value 33.3% (95% CI, 4.3-77.7%), and negative predictive value of 69.6% (95% CI, 64.6-74.3%).

Conclusion: Fasting glucose on PPD1 was not associated with persistent insulin resistance at 4 to 12 weeks postpartum.