A CONTROLLED TRIAL OF NATURAL CYCLES WITH AND WITHOUT GnRH ANTAGONIST ADMINISTRATION IN POOR RESPONDER WOMEN: PRELIMINARY RESULTSXydias G., Liarmakopoulou S., Argyriou A., Sarella A., Dimaki A., Pappa H.Diagnosis-IVF Department, 166 Alexandras Av., Athens, Greece INTRODUCTION Although the first pregnancy in assisted reproduction was achieved in a natural (unstimulated) cycle (NC), many IVF units have abandoned this method because it has been judged as inefficient therapy. Efficacy of NC IVF is hampered by high cancellation rates because of premature luteinizing hormone (LH) rise and premature ovulations. Furthermore, NC has many difficulties in programming oocyte retrievals. However, the advantages might overcome these problems, so scientists are motivated to find solutions. GnRH-antagonist induce a reversible medical hypophysectomy which prevents the occurrence of premature LH surges and allows the programming of treatment cycles as mentioned in other studies. DESIGN The aim of this study was to compare the results of natural cycles with and without the use of a single dose of GnRH-a. Thus, group I patients underwent 143 IVF NCs (control group) and group II patients performed 22 IVF NCs supported with GnRH-a. MATERIAL AND METHODS Both groups were monitored daily or every two days ultrasound follicular measurements and whenever a follicle diameter 15±1mm was scanned, daily assessment of E2 and LH levels occurred. In group I, when LH measurement was 7-12 IU/l and the follicle diameter 17mm, 6500 IU of hCG were administered the same evening and oocyte retrieval was performed 35 hours later. In group II, when LH measurement was 7-12 IU/l but the follicle diameter was less than 16mm, then a single injection of 0,25 mg Cetrorelix was administered. The next evening 6500 IU of hCG were administered and the oocyte retrieval was performed 35 hours later. ICSI was performed in all cases. RESULTS 84 patients underwent 143 cycles in group I. 13 patients underwent 22 cycles in group II. Mean age at treatment was 37,59±4,29 and 38,77±1,82 for groups I and II respectively. The main cause of infertility was poor responding in gonadotropin’s stimulation (95,8% and 95,5% respectively). Lower rate of cancellation was observed in group II. Successful oocyte retrievals were achieved in 71,3% in group I and 86,4% in group II. Retrieval of mature oocytes was accomplished in 79,05% in group I and 89,5% in group II. Fertilization rate was 75,90% in group I and 82,40% in group II. Normal fertilization resulting in embryo transfer occurred in 54,90% in group I and 68,42% in group II. Pregnancy rates per starting cycle and per embryo transfer were also higher in group II (11,12% vs 18,18% and 28,60% vs 30,80% respectively). CONCLUSIONS Poor responders may benefit from NC because it is associated with a close to zero multiple pregnancy rate and no risk of ovarian hyperstimulation syndrome. Furthermore, NC is less time consuming, physically and emotionally less demanding for patients and cheaper than stimulated IVF. Our study showed better results with the administration of GnRH-a, however none of these observations has shown statistically significant difference. Thus, more cases must be done in order to lead us to a conclusion. It is really important though that the use of GnRH-a in NCs is effective in order to have a better control of LH surge and a better schedule of oocyte retrieval.