Serum Oestradiol Pattern during Coasting is Different in Antagonist Cycles Compared with Long Agonist Cycles in In Vitro Fertilisation

Background: GnRH agonists and antagonists have different mechanism of action, and therefore serum estradiol levels might differ during coasting in IVF. Aims: To compare the change in serum oestradiol levels after withholding the gonadotropins for coasting between long agonist and antagonist cycles. Study Design: Retrospective study. Methods: Antagonist and long agonist cycles, in which coasting was performed, were analysed in this retrospective analysis. Antagonist cycles (n=50) were compared with long agonist cycles (n=52) with respect to daily serum oestradiol levels following withholding of gonadotropins. Results: The pattern of change in serum oestradiol was different between groups; it increased on the first day by 11.2% and decreased thereafter on the second and third days in the agonist group. However, it began to decrease from the first day in the antagonist group. Therefore, peak serum oestradiol levels were significantly higher in the agonist group than in the antagonist group (mean±standard deviation; 5798±1748 vs 5104±1351 pg/mL). The duration of coasting was shorter in the antagonist group compared with that in the agonist group (mean ±standard deviation; 2.60±1.40 vs 1.96±0.88 days). Conclusion: Serum oestradiol pattern during coasting is different in antagonist cycles compared with long agonist cycles in in vitro fertilisation.