Longitudinal patterns of maternal serum C-peptide change in pregnancy (A and B) with more detail of women in pattern 3 (C). Pattern 1: undetectable maternal serum C-peptide throughout pregnancy. Pattern 2: detectable maternal serum C-peptide at 12 weeks’ gestation. Pattern 3: undetectable maternal serum C-peptide at 12 and 24 weeks, which became detectable at 34 weeks’ gestation.