VEGFA and polycystic ovary syndrome: When Th1 cytokines are overexpressed, it will lead to abortion.[54] TGF-β1 is a Th2-type cytokine that regulates uterine blood flow and the expression of vascular endothelial growth factor, promotes endometrial tolerance and contributes to embryo implantation, thereby affecting the outcome of pregnancy.[55] Moreover, single nucleotide polymorphism of the TGF-β1 gene is associated with polycystic ovary syndrome in Chinese women.[27] Increased levels of TGF-β1 and level reduction of TGF-β1 receptors may lead to polycystic ovary syndrome and ovarian hyperstimulation.[56,57]