Our finding of a positive association between prolactin levels and GDM risk in pregnancy is in line with findings among non-pregnant populations with prolactinoma, where elevated prolactin levels above the normal range (i.e., hyperprolactinemia) were associated with adverse metabolic outcomes including hyperinsulinemia (6), insulin resistance (6–8), and increased body weight (9, 10), and normalizing prolactin levels reverted the adverse metabolic outcomes (8–10); these findings support a role of hyperprolactinemia in worsening metabolic outcomes. Here, PRL is linked to hyperprolactinemia.