Increased Molar Proinsulin-to-Insulin Ratio in Women With Previous Gestational Diabetes Does Not Predict Later Impairment of Glucose Tolerance

OBJECTIVE To evaluate if an increased proinsulin-to-insulin ratio (PI/I) in former gestational diabetes mellitus (GDM) subjects could be a marker for later impairment of glucose tolerance. RESEARCH DESIGN AND METHODS This study is a prospective follow-up. In a previous follow-up study of former GDM subjects 3–4 years after an index pregnancy, an increased PI/I was found also in normoglycemic nonobese former GDM subjects compared with control subjects. A 75–g oral glucose tolerance test (OGTT) was performed 3 years after the first follow-up, i.e., 6–7 years after the index pregnancy in 97 of the former GDM subjects and in 23 control subjects. A 75-g OGTT according to the World Health Organization was performed. Glucose, insulin, proinsulin, and C-peptide were determined at 0, 30, 60, 90, 120, 150, and 180 min after the glucose intake. RESULTS Since the first follow-up, an additional 3 in 97 (3.1%) and 15 in 97 (15.5%) of the former GDM subjects had NIDDM or impaired glucosetolerance (IGT), respectively. All control subjects still had a normal OGTT. The fasting PI/I at follow-ups 1 and 2 was significantly correlated in the former GDM subjects ( r = 0.41, P r = 0.46, P CONCLUSIONS The hypothesis that an increased fasting PI/I is a marker for later development of NIDDM or IGT in former GDM subjects could not be supported.