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Eur J Obstet Gynecol Reprod Biol. 2005 Jun 1;120(2):185-9.

A randomised study of GnRH antagonist (cetrorelix) versus agonist (busereline) for controlled ovarian stimulation: effect on safety and efficacy.

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Unidade de Reprodução Medicamente Assistida, Departamento de Ginecologia e Obstetrícia, Hospital de São João, Faculdade de Medicina do Porto, Portugal.



To assess safety and efficacy of cetrorelix utilisation in controlled ovarian stimulation (COS).


Phase III, randomized, single center study of 131 patients undergoing COS and IVF with or without ICSI, in a University affiliated Hospital. Sixty-six patients were allocated to the protocol with antagonist and 65 to the agonist protocol arm. The Student's t-test, the Mann-Whitney test and the chi-square test were applied as required, using SPSS for Windows with a two-sided 5% significance level.


The mean (+/-S.D.) duration of stimulation was 9.5+/-1.7 days in the antagonist group and 10.6+/-2.1 days in the agonist group (P=0.02). The mean (+/-S.D.) duration of suppression was 4.6+/-1.3 days in the antagonist group and 27.3+/-5.2 days in the agonist group (P<0.0001). No significant differences were noted in other outcome measures: amount of rFSH required, estradiol level on hCG day, number of follicles>or=15 mm and endometrial thickness on oocyte retrieval day, number of oocytes retrieved, fertilization rate and number of OHS cases. Clinical pregnancy rates per-attempt and per-transfer were 15.1% and 17.0% in the antagonist group and 16.9% and 20.0% in the agonist group (P=0.79 and 0.71, respectively).


GnRH antagonists are an effective, safe and well tolerated alternative to agonists for COS.

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