Probiotics were the most common and effective interventions at reducing gestational diabetes risk (fasting blood glucose with the mean difference (MD) = −2.92, −0.05; I2 = 45, 98.97), fasting serum insulin (MD = −2.3, −2.06; I2 = 45, 77), glycated haemoglobin (Hb A1c) = −0.16; I2 = 0.00)), Homeostatic Model Assessment of insulin resistance (HOMA-IR) (MD = −20.55, −0.16; I2 = 0.00, 72.00), and lipid metabolism (MD = −5.47, 0.98; I2 = 0.00, 90.65). The gene discussed is GSTM1; the disease is Insulin resistance.