Study design and participants
A retrospective study of infertile women with normal ovarian reserve attending the Assisted Reproduction clinic, Shanghai First Maternity and Infant Hospital for IVF from January 2018 to December 2018 was undertaken. Ethical approval was not required for the retrospective analysis.
Women were included if they fulfilled the following inclusion criteria: (i) less than 40 years of age; (ii) having indications for IVF; (iii) regular menstrual cycles over the previous 3-month period (25–35 days in duration); (iv) antral follicle count (AFC) of more than 5 on menstrual cycle day 2–3, and basal serum FSH concentration of no more than 10 IU/L. Women were excluded if they had: (i) diagnosis of polycystic ovarian syndrome, (ii) an abnormal uterine cavity shown on hysterosalpingogram or hysteroscopy, (iii) moderate or severe endometriosis, (iv) use of donor eggs/sperm, (v) preimplantation genetic testing for aneuploidy, (vi) rescue intracytoplasmic sperm injection (ICSI) or half ICSI or (vii) antagonist cycles with fresh embryo transfer.
Women were offered either progestin-primed ovarian stimulation protocol (PPOS group) or antagonist protocol (antagonist group) at the discretion of the attending physicians or subject to the wishes of the couple.