Trigger injection

A trigger injection is a medicine given at a precisely timed point near the end of ovarian stimulation to complete the final maturation of eggs and, in IUI or timed intercourse cycles, to bring on ovulation at a predictable time. In IVF, egg retrieval is scheduled a set number of hours after the trigger, before ovulation would naturally occur, so that mature eggs can be collected directly from the follicles. Different trigger approaches exist, including hCG-based triggers, GnRH-agonist triggers (sometimes used in antagonist protocols, particularly to reduce OHSS risk), and dual triggers combining both. The choice of trigger is made by the treating fertility specialist based on the stimulation protocol used and the individual's risk factors, including OHSS risk. This entry does not describe specific doses or timing details, which are set individually.

Also known as: hCG trigger, agonist trigger, dual trigger

Last reviewed: 9 September 2026. Written by the Antega Editorial Team. General information only — always follow the advice of your own clinic, doctor or pharmacist.