Five placentae samples for each group were collected and dissected from the middle cross section of villus tree within 15 min of the delivery. To compensate for intra-placental variability, we collected 3 independent samples per placenta giving a total of 15 GDM and 15 control samples. Tissue was bluntly dissected to remove visible connective tissue, blotted dry on filter paper, snap frozen in liquid nitrogen, and stored at −80°C. Small pieces of tissues were embedded in optimal cutting temperature compound (Tissue-Tek; Sakura Finetek USA) and kept at −80°C until cryosection.