Withholding gonadotropins until human chorionic gonadotropin administration.

Withholding gonadotropins in women who exhibit high estradiol responses before follicles reach full maturation is called "coasting." Coasting, or suspending gonadotropin administration, can be an effective strategy for decreasing the risk of ovarian hyperstimulation syndrome (OHSS) while reducing cancelation rates. In in vitro fertilization cycles, mechanistically it is believed that withholding gonadotropins starves smaller follicles, induces apoptosis, and decreases the potential for these follicles to elaborate vascular endothelial growth factor, a known mediator of OHSS. It is generally accepted that coasting should be initiated when the estradiol (E₂) level is >3000 pg/mL in the setting of immature follicles. The human chorionic gonadotropin (hCG) trigger should be administered when the E₂ level subsequently drops to a "safe" level. Cycle cancellation should be considered if, after 3 to 4 days of coasting, the E₂ level remains excessively elevated. Oocyte retrieval may also be cancelled if the E₂ level on the day after hCG trigger drops precipitously. In gonadotropin-releasing hormone agonist (GnRHa)-based protocols, one can consider withholding GnRHa administration if the E₂ level continues to increase after a few days of coasting. Current data seem to show that the coasting period is short and/or is less likely to be required in GnRH-antagonist protocols as compared with GnRHa-based protocols. Large randomized control trials are still needed to establish the relative efficacy of coasting versus embryo cryopreservation in the context of OHSS prevention.