SLC16A3 and lactic acidosis: The possible reason for the polarity of MCT1 and MCT4 in the placenta is that the expression of MCT4 in the maternal surface of the SCT promotes the excretion of lactic acid, which facilitates lactate efflux, helps to maintain placental and fetal pH during times of glycolytic stress and prevents lactic acidosis from occurring in the fetal circulation (95).