In a cohort, Wu et al. studied pregnant women between 12 and 16 weeks’ gestation and identified differential methylation in five CpGs within the constitutive photomorphogenic homolog subunit 8 (COPS8), phosphoinositide-3-kinase, regulatory subunit 5 (PIK3R5), 3-hydroxyanthranilate 3,4-dioxygenase (HAAO), coiled-coil domain containing 124 (CCDC124), and chromosome 5 open reading frame 34 (C5orf34) genes in women who developed GDM relative to matched healthy pregnancies. Here, HAAO is linked to gestational diabetes.