Menstruation-free interval and ongoing pregnancy in IVF using GnRH antagonists

BACKGROUND: The purpose of this study was to evaluate prospectively the association between the achievement of ongoing pregnancy and the time interval from the end of menstruation until the administration of HCG (menstruation-free interval) in patients treated by IVF. METHODS: A fixed dose of 200 IU of recombinant FSH (rFSH) was started in 90 patients on day 2 of the menstrual cycle and daily GnRH antagonist was initiated on day 6 of stimulation. Triggering of final oocyte maturation was performed with 10,000 IU of HCG as soon as three follicles of > or =17 mm were present at ultrasound. RESULTS: Single embryo transfer was performed in 64.6% of the patients who reached embryo transfer (53/82). Ongoing pregnancy rate per embryo transfer was 18.3% (95% CI 11.4-28.0%). The menstruation-free interval significantly predicted the probability of ongoing pregnancy in a logistic regression analysis, controlling for female age and LH on day 1 of stimulation (odds ratio for the menstruation-free interval: 0.70; 95% CI: 0.54-0.92). CONCLUSION: The longer the interval from the end of menstruation until the administration of HCG, the lower the probability of ongoing pregnancy in patients stimulated with recombinant FSH and GnRH antagonist for IVF.