Revival of the natural cycles in in-vitro fertilization with the use of a new gonadotrophin-releasing hormone antagonist (Cetrorelix): a pilot study with minimal stimulation.

Natural cycles were abandoned in in-vitro fertilization (IVF) embryo transfer, due to premature luteinizing hormone (LH) surges--and subsequent high cancellation rates. In this study, we investigated the administration of a new gonadotrophin-releasing hormone antagonist (Cetrorelix) in the late follicular phase of natural cycles in patients undergoing IVF and intracytoplasmic sperm injection (ICSI). A total of 44 cycles from 33 healthy women [mean age 34.1 +/- 1.4 (range 26-36) years] were monitored, starting on day 8 by daily ultrasound and measurement of serum concentrations of oestradiol, LH, follicle stimulating hormone (FSH) and progesterone. When plasma oestradiol concentrations reached 100-150 pg/ml, with a lead follicle between 12-14 mm diameter, a single injection (s.c.) of 0.5 mg (19 cycles) or 1 mg (25 cycles) Cetrorelix was administered. Human menopausal gonadotrophin (HMG; 150 IU) was administered daily at the time of the first injection of Cetrorelix, and repeated thereafter until human chorionic gonadotrophin (HCG) administration. Four out of 44 cycles were cancelled (9.0%). No decline in follicular growth or oestradiol secretion was observed after Cetrorelix administration. A total of 40 oocyte retrievals leading to 22 transfers (55%) was performed. In 10 cycles (25%), no oocyte was obtained. Fertilization failure despite ICSI occurred in six cycles (15%). In two patients the embryo was arrested at the 2 pronuclear (PN) stage. The stimulation was minimal (4.7 +/- 1.4 HMG ampoules). A total of seven clinical pregnancies was obtained (32.0% per transfer, 17.5% per retrieval), of which five are ongoing. Thus, a spontaneous cycle and the GnRH antagonist Cetrorelix in single dose administration could represent a first-choice IVF treatment with none of the complications and risks of current controlled ovarian hyperstimulation protocols, and an acceptable success rate.