Polycystic ovary syndrome (PCOS) is associated with lower pregnancy rate and higher miscarriage rate in assisted reproductive technologies.The uterine dysfunctions have been fiercely discussed.In this article we threw light on the follicular progesterone profile in antagonist protocol for PCOS patients.We discovered that: (1)On trigger day,PCOS patients showed higher plasma level of luteinizing hormone (LH) than controls,while on follicle aspiration day,PCOS patients showed significantly lower follicular P4 level than controls,yet both groups obtained similar oocytes outcomes except for the significantly lower viable embryo rates in PCOS patients.(2) However,PCOS subgroup with relatively lower follicular progesterone level on aspiration day resulted in significantly higher viable embryo rate than PCOS patients with higher follicular progesterone level and non-PCOS controls,and the blastocyst formation rate is significantly higher in lower follicular progesterone PCOS subgroup than healthy controls.PCOS patients with higher follicular progesterone level exhibited similar follicular progesterone level with non-PCOS patients but the viable embryo rate is dramatically lower.We concluded that PCOS patients showed lower follicular progesterone level,and that while PCOS compromises early embryo quality the reduction of follicular progesterone level on aspiration day in PCOS women is associated with better early embryo development,and may thus represent a protective mechanism for oocytes quality within PCOS physiological process.