Ovarian stimulation
Women started their IVF with ovarian stimulation using either PPOS or long agonist protocols. For the long agonist protocol, gonadotropin-releasing hormone analogue (GnRHa) (1.88mg Triptorelin acetate, Diphereline, Ipsen Pharma Biotech, France) was given for pituitary desensitisation from the mid-luteal phase in the previous cycle. On Day 2–3 of the menstrual cycle, they underwent transvaginal ultrasound examination and serum oestradiol measurement. Human menopausal gonadotrophin (hMG) (Lebaode, Lizhu, china) or recombinant FSH (Puregon, Organon, Dublin, Ireland or Gonal F, Merck Serono S.p.A, Modugno, Italy) was given at 150–225 IU per day based on the antral follicle count (AFC), age of women and previous ovarian response, according to the standard operation procedures of the centre. For the PPOS protocol, Medroxyprogesterone MPA (MPA, 10 mg/d, Shanghai Xinyi Pharmaceutical Co., China) was also given from day of the ovarian stimulation until the day of ovulation trigger. Ovarian response was monitored by serial transvaginal scanning with or without hormonal monitoring. Further dosage adjustments were based on the ovarian response at the discretion of the clinicians in charge.
When three leading follicles reached ≥18 mm in diameter, Ovidrel 250 microgram (Merck Serono S.p.A., Modugno, Italy) or triptorelin (0.1 mg; Decapeptyl, Ferring Pharmaceuticals, Netherlands) and hCG (2000 IU; Lizhu Pharmaceutical Trading Co., China) were given to trigger final maturation of oocytes. Oocyte retrieval was performed around 36 hours later.