Study procedures
Eligible women were indicated for IVF or ICSI. A long or short protocol with the use of a gonadotropin-releasing hormone (GnRH) agonist, or a protocol with a GnRH antagonist, or a mild stimulation protocol was applied for controlled ovarian stimulation according to women’s age, BMI and ovarian reserve function. The ovarian stimulation protocols in our center had been described in detail previously(17). Follicular growth was monitored by ultrasound and as soon as at least 2 follicles with diameters ≥ 18 mm were detected, an hCG trigger for final oocyte maturation was given. Then transvaginal ultrasound-guided oocyte retrieval was performed 34–36 h after hCG administration.
Conventional IVF or ICSI was performed according to the male partner’s semen quality in laboratory. Good-quality embryos were selected for transfer at cleavage-stage according to Puissant criteria(18) or at blastocyst stage according to Gardner criteria (19).
Luteal-phase support was performed on the day of oocyte retrieval or on the day of endometrial transformation, and continued until 12 weeks of gestation. Different luteal-phase support regimens were adopted for embryo transfer in our center, including oral dydrogesterone (20 mg, twice a day) alone, oral dydrogesterone (20 mg, twice a day) combined with utrogestan vaginal capsules (200 mg, once a day) or crinone 8% vaginal gel (90 mg, once a day).
Biochemical pregnancy was determined when a serum human chorionic gonadotropin (hCG) level reached 25 mU per milliliter at 14 days after embryo transfer (ET). Clinical pregnancy was confirmed when a gestational sac by transvaginal ultrasound was observed at 3-4 weeks after a positive hCG test. Biochemical pregnancy loss was defined as spontaneous pregnancy demise based on a previous positive pregnancy test that then becomes negative with no gestational sac observed through an ultrasound evaluation. EM was defined as a termination of pregnancy before 12 weeks of gestational age in this study. The preterm birth was defined as a successful delivery before 37 gestational weeks and live birth was defined as the birth of at least one living baby after 37 weeks of gestation.