The continuation of studies in the perinatal period showed that both the maternal and cord serum irisin levels at term delivery were at the same level regardless of glycemic status: for mothers with GDM values, they were 1524 (1261–1783) ng/mL vs. 1723 (1460–1988) ng/mL, respectively; and for mothers with non-GDM, the values were 1375 (1084–1652) ng/mL vs. 1257 (1153–1415) ng/mL, respectively. The gene discussed is FNDC5; the disease is gestational diabetes.