Diabet. Med. 29, e361–e364 (2012)
Aims There are previous suggestions of increased C-peptide concentration in women with Type 1 diabetes during pregnancy. Our aim was to re-evaluate the hypothesis of a pregnancy-induced increase by measuring plasma C-peptide concentration in women with stable blood glucose control under standardized fasting and meal-stimulated conditions.
Methods Ten women with Type 1 diabetes; median age 31.1 years, median diabetes duration 19 years, median HbA1c 52 mmol/mol (6.9%) were admitted to a clinical research facility for two 24-h visits in early (12–16 weeks) and late (28–32 weeks) pregnancy. Women They ate standardized study meals - 80-g carbohydrate dinner, 60-g carbohydrate breakfast, and fasted between meals and overnight. Closed-loop insulin delivery maintained stable and comparable glycaemic conditions. Paired samples for plasma glucose and C-peptide were obtained.
Results Plasma glucose levels were comparable in early (median 6.5 mmol/l; interquartile range 5.6–8.6) and late pregnancy (median 7.0 mmol/l; interquartile range 6.1–7.8; P = 0.72). There was no change in fasting or meal-stimulated plasma C-peptide concentration from early to late pregnancy; mean difference 4.0 pmol/l (95% CI −6.0 to 7.0; P = 0.9). Four women had detectable C-peptide; peak (range) early vs. late pregnancy 48.5 (10–115) vs. 40.0 pmol/l (80–105); P = 0.5, which was weakly associated with plasma glucose; R2 = 0.15, P < 0.0001.
Conclusions We found no gestational changes in plasma C-peptide concentration. Previously reported increases may reflect differences in glucose control and/or exogenous insulin doses. This study highlights the importance and challenges of standardizing experimental conditions for accurate plasma C-peptide measurement during Type 1 diabetes pregnancy.