GnRH agonist triggers and their use in assisted reproductive technology: the past, the present and the future.

Gonadotropin releasing hormone agonist triggers are very effective in eliminating early-onset ovarian hyperstimulation syndrome (OHSS). However, in most studies they result in inferior pregnancy rates compared to hCG triggers in fresh autologous transfers. This is not due to an effect on embryo quality but rather due to inadequate corpus luteum formation and a defective luteal phase causing poor implantation. Intensive and adjusted steroid support or low-dose hCG may correct this. Late-onset OHSS is eliminated by using a freeze-all strategy. Pregnancy rates after transfer of thawed vitrified embryos are consistently high. A strategy combining a gonadotropin releasing hormone agonist trigger with vitrification of all embryos has been proposed as a means of achieving a truly OHSS-free clinic.