A Cochrane review [Abstract] 1 included 22 studies with a total of over 3000 women undergoing endometrial preparation for embryo transfer with frozen embryos or embryos derived from donor oocytes. No significant benefit in pregnancy rate was demonstrated when using GnRH agonists vs control (5 studies, n=778). However , the only study assessing the live birth rate showed better result with nasal buserelin compared to no GnRH agonist (OR 2.62, 95% CI 1.19 to 5.78, n=234). No evidence of statistically significant benefit was found for one GnRH agonist over another, or vaginal over intramuscular progesterone administration. No difference in pregnancy rate was demonstrated when no treatment was compared to steroids, ovarian stimulation, or human chorionic gonadotropin (hCG) prior to embryo transfer, although using hCG several times before the oocyte retrieval decreases the pregnancy rate. Starting progesterone either on the day of oocyte pick-up (OPU ) or the day after OPU showed better results in clinical pregnancy rates than starting the day before OPU (OR 1.87, 95% CI 1.13 to 3.08; I2 = 0%; 1 trial, n=282).
Comment: The quality of evidence is downgraded by study quality (unclear allocation concealment in most of the studies), by inconsistency (heterogeneity in interventions and outcomes), and by indirectness (only 4 studies assessed the live birth rate).
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