Pancreatic B-cell function during normal pregnancy.

24-h urinary C-peptide excretion was studied in 19 healthy normal weight women with normal glucose tolerance, and related to weight gain and skinfold thickness at 12, 20, 30, 36 weeks of gestation and 6-8 weeks post partum. The urinary C-peptide values (total nmoles or nmoles per kg body weight) showed a significant and progressive increase with gestation. The average C-peptide value was already at 12 weeks of gestation 4 times higher than under non-pregnant conditions. The urinary C-peptide excretion was neither related to maternal weight, weight gain or skinfold thickness at any of the observation periods during pregnancy, nor to the plasma C-peptide response to an oral glucose load at 32 weeks of gestation. A significant correlation was found between urinary C-peptide excretion and body weight determined post partum (r = 0.54, p less than 0.05). The increment in urinary C-peptide excretions at 12 weeks of gestation was unrelated to body mass, suggesting that insulin resistance is present already at this early stage of normal gestation.