The gonadotropins used for controlled ovarian stimulation (COS) were human menopausal gonadotropin (Ferring Pharmaceuticals, Tokyo, Japan or ASKA Pharmaceutical, Tokyo, Japan) or recombinant FSH (Gonal‐f®; Merck Serono, Tokyo, Japan). The long protocol started with administration of nasal buserelin 600 μg/day (Buserecur®; Fuji Pharma, Tokyo, Japan) on the prestimulation cycle day 21. The short protocol started with administration of nasal buserelin 600 μg/d on the stimulation cycle day 3. In both the long and short protocols, a GnRH agonist was daily administered until the day of hCG injection. For the GnRH antagonist protocol, alternate‐day (in principle) administration of a GnRH antagonist (ganirelix [Ganirest®, MSD, Tokyo, Japan] or cetrorelix [Cetrotide®, Merck Serono]) began when follicular size reached a diameter of 14 to 16 mm or when a premature luteinizing hormone (LH) surge was suspected based on blood LH levels, followed by final oocyte maturation with a GnRH agonist or hCG (3000‐5000 IU). After 34‐36 hours of hCG injection, the mature oocytes were retrieved transvaginally, depending on follicular diameter, serum E2 and AMH levels, and patient's age. The retrieved oocytes were then fertilized by conventional IVF or ICSI. Split insemination was selected in cases of ≤6 metaphase II (MII) oocytes or oligozoospermia (defined as sperm concentrations post swim up ≤10 × 106/mL). Fresh embryo transfer was conducted, if all the following criteria were met: (a) serum E2 level on the day of hCG injection was ≤6000 pg/mL, (b) the serum P4 level on the day of hCG injection was ≤1.5 ng/mL, and (c) no signs of OHSS were noticed after oocyte retrieval.