Determinants of Mild Gestational Hyperglycemia and Gestational Diabetes Mellitus in a Large Dutch Multiethnic Cohort

Abstract

OBJECTIVE—The purpose of this study was to identify independent determinants of mild gestational hyperglycemia (MGH) and gestational diabetes mellitus (GDM) and to assess the correlation between fasting glucose and C-peptide levels among control, MGH, and GDM women. RESEARCH DESIGN AND METHODS—A total of 1,022 consecutive women were evaluated with a 1-h 50-g glucose challenge test (GCT) at between 16 and 33 weeks of gestation. Women with a capillary whole-blood glucose ≥7.8 mmol/l in the GCT underwent a 3-h 100-g oral glucose tolerance test (OGTT). On the basis of a positive GCT, the women with a positive OGTT were classified as GDM, whereas the women with a negative OGTT were classified as MGH. The following data were collected for all women: age, prepregnancy BMI, ethnicity, clinical and obstetric history, pregnancy outcome, and C-peptide level. RESULTS—A total of 813 women (79.6%) were normal, 138 (13.5%) had MGH, and 71 (6.9%) had GDM. There was a stepwise significant increase in mean fasting glucose (3.6 ± 0.4, 3.9 ± 0.4, and 4.7 ± 0.7 mmol/l, respectively) and C-peptide level (0.60 [0.1–2.4], 0.86 [0.3–2.0], and 1.00 [0.5–1.6] nmol/l, respectively) among the three diagnostic groups. Maternal age, non-Caucasian ethnicity, and prepregnancy BMI were associated with GDM, whereas only maternal age and prepregnancy BMI were associated with MGH. A positive correlation between levels of fasting glucose and C-peptide was found in control women (r = 0.39 [95% CI 0.31–0.46]). A similar result was seen in MGH women (r = 0.38 [95% CI 0.23–0.52]), whereas the correlation between fasting glucose and C-peptide was nearly lost in GDM women (r = 0.14 [CI −0.09 to 0.36]). The fasting C-peptide–to–glucose ratio was reduced by 60% in GDM patients versus control subjects and MGH patients (0.41 ± 0.25 vs. 0.70 ± 0.20 and 0.73 ± 0.23, P < 0.001). CONCLUSIONS—Of the well-known independent determinants of GDM, only maternal age and prepregnancy BMI were associated with MGH. It appears that additional factors promoting loss of β-cell function distinguish MGH from GDM. One of these factors appears to be ethnicity.