This randomized trial aims to compare the euploid rate of blastocysts between PPOS (progestin-primed ovarian stimulation) and GnRH (gonadotrophin releasing hormone) antagonist protocols in patients with PCOS (polycystic ovary syndrome) undergoing PGT-A (preimplantation genetic testing for aneuploidy). Infertile women with PCOS will be recruited for study after explanation and counseling if they fulfill the inclusion criteria and do not have the exclusion criteria. Eligible women will be randomised into one of the two groups:

Antagonist group: Women will receive antagonist once subcutaneously daily from day 6 of ovarian stimulation till the day of the ovulation trigger.

PPOS group: Women will receive oral MPA (medroxyprogesterone acetate)10mg qd from Day 3 till the day of ovulation trigger.

The primary outcome is the euploidy rate of blastocysts.

Inclusion Criteria:

• Women age between 20 and 37 years.
• Women diagnosed with PCOS according to the modified Rotterdam criteria: oligomenorrhea or amenorrhea, together with the presence of ≥12 antral follicles (≤9 mm) and/or ovarian volume >10 mL on transvaginal ultrasonographic scanning, and/or clinical/ biochemical hyperandrogenism. Other causes of hyperandrogenism and ovulation dysfunction-including tumours, congenital adrenal hyperplasia, hyperprolactinaemia and thyroid dysfunction-were excluded

Exclusion Criteria:

• Presence of a functional ovarian cyst with E2>100 pg/mL
• Endometriosis grade 3 or higher
• Repeated implantation failure (>=4 embryos replaced or >=2 blastocysts replaced without success)
• Women with a uterine cavity abnormality, such as a uterine congenital malformation (uterus uni-cornate, bicornate, or duplex); untreated uterine septum, adenomyosis, submucous myoma, or endo-metrial polyp(s)
• Women who are indicated and planned to undergo PGT-SR (Preimplantation genetic testing for structural rearrangement) or PGT-M (Preimplantation genetic testing for monogenic disorder), for example, parental abnormal karyo-type or diagnosed with monogenic disease;
• Recipient of oocyte donation
• Presence of hydrosalpinx which is not surgically treated

Individual participant data that underlie the results after deidentification (text, tables, figures, and appendices) and study protocol will be shared.

Data will be available when beginning 3 months and ending 5 years following article publication.

To achieve aims in the approved proposal, researchers who provide a methodologically sound proposal will be shared with. Proposals should be sent to lihe198900@163.com.