The purpose of this study is to assess whether the probability of pregnancy is dependent on the duration of GnRH agonist downregulation in IVF cycles.

GnRH agonists have been used extensively in assisted reproduction technologies for inhibition of gonadotropin secretion from the pituitary prior to initiation of ovarian stimulation. Administration of GnRH agonists results in the prevention of spontaneous LH surges, which lead to luteinization of the developing follicles, initiation of final oocyte maturation and a decrease in pregnancy rates.

GnRH agonists are usually administered according to two protocols: the short and long protocol.In the long protocol, downregulation with GnRH agonists is initiated either in the middle of the secretory phase, or at the beginning of the follicular phase. Stimulation of the ovaries with gonadotropins is initiated when downregulation is confirmed.

Administration of gonadotropins is usually started during the second or third week of treatment with GnRH agonists.The possibility of earlier initiation of the ovarian stimulation, if downregulation is confirmed at an earlier stage, has not been examined so far.

The purpose of this study is to assess whether the duration of pituitary downregulation with GnRH agonists, prior to initiation of ovarian stimulation with gonadotropins, has any effect on pregnancy rate, in women undergoing IVF.

Inclusion Criteria:

• age under 39
• less than 3 previous IVF cycles
• BMI 18-29
• normal ultrasound of internal genital organs

Exclusion Criteria:

• polycystic ovarian syndrome
• endometriosis