Why is GnRH antagonist used in ovarian stimulation?

Stimulation medicines encourage several ovarian follicles to develop. As follicles grow, the body may release a natural luteinising hormone surge. If that surge happens before the fertility team is ready, ovulation can occur earlier than planned. A GnRH antagonist blocks the relevant GnRH signal quickly, giving the clinic more control over the timing of final egg maturation and collection.

It is usually introduced during stimulation according to the protocol rather than used continuously from the start. Scan results, hormone levels, follicle development, and the planned procedure determine when it is given. You can read about the medicine in [GnRH Antagonist](/materials/gnrh-antagonist/).

Follow the injection schedule closely and attend monitoring visits. Mild redness, itching, or soreness where the injection was given may occur. Report new symptoms, allergies, or any difficulty using the device to the fertility team.

Do not double a missed dose unless the clinic specifically tells you to do so. A timing change can affect the stimulation plan, so contact the team as soon as you realise a dose was missed or delayed.

Contact the clinic for significant abdominal discomfort, increasing bloating, nausea, or vomiting during stimulation. Get urgent medical help for severe pelvic pain, heavy bleeding, breathing difficulty, faintness, or markedly reduced urine. These symptoms require prompt assessment and may not be caused by the antagonist itself.

Ask what day to start the antagonist, how long to continue it, and how scans or blood tests decide the next dose. Clarify what to do if the injection is late, which reactions are expected, and how to reach the team urgently.