INS and hyperinsulinism: Recent work in the CONCEPTT cohort identified that pregnancies with the most hyperinsulinaemic offspring had a third-trimester increase in C-peptide in maternal blood, unexpected in women with no evidence of beta cell function at baseline, providing an opportunity to assess C-peptide as a potential biomarker for fetal hyperinsulinism [42], or fragments of C-peptide, insulin or proinsulin [43].