First Trimester Maternal Glycated Hemoglobin and Sex Hormone–Binding Globulin Do Not Predict Third Trimester Glucose Intolerance of Pregnancy

Abstract

Early pregnancy prediction of third trimester glucose intolerance may identify a population of women whose trajectory toward gestational diabetes mellitus (GDM) is modifiable. We assessed whether first trimester glycated hemoglobin (HbA1c) and sex hormone–binding globulin (SHBG), markers of insulin resistance, predicted third trimester glucose intolerance. Nondiabetic women with singleton pregnancies enrolled in a prospective observational study, 11 0/7 to 14 6/7 weeks. At enrollment, maternal characteristics, medical history, and blood samples were collected for HbA1c and SHBG. Two-step GDM screening was performed, 22 0/7 to 33 6/7 weeks. A 50 g oral glucose tolerance test ≥130 mg/dL defined screen positive, or glucose intolerance. Carpenter-Coustan criteria diagnosed GDM. Means HbA1c and SHBG were compared between glucose-intolerant versus normoglycemic women, and GDM versus no GDM women. We report unadjusted and adjusted odds ratios (OR; 95% confidence interval [CI]) of regression analyses. Adjusted models include race, enrollment body mass index, and history of GDM. Among 250 women, 29% were glucose intolerant and 6% had GDM. Among glucose-intolerant women, HbA1c was higher (5.3 ± 0.3 vs. 5.1 ± 0.3, P = .01) and associated with glucose intolerance in unadjusted, but not adjusted, models (OR: 2.9, 95% CI: 1.2-7.1; adjusted odds ratio [aOR]: 2.0, 95% CI: 0.7-5.4). Among GDM women, HbA1c was higher (5.4 ± 0.4 vs 5.2 ± 0.3, P = .002) and SHBG was lower (228 ± 72 vs 288 ± 93 mmol/L, P = .02). The HbA1c predicted GDM in unadjusted (OR: 13.2, 95% CI: 2.6-68.0) but not adjusted (aOR: 6.7, 95% CI: 0.8-55.2) models. Although metabolic alterations may well precede third trimester glucose intolerance, neither HbA1c of SHBG remained an independent predictor of glucose intolerance or GDM in adjusted models.