Fertility Glossary

Trigger injection

The timed injection that matures the eggs before retrieval.

Medicines & protocols

The trigger — hCG, a GnRH agonist, or both — completes egg maturation. Retrieval is scheduled around 34 to 36 hours later, so timing must be exact; a missed or mistimed trigger can mean no eggs are collected. An agonist trigger is used where OHSS risk is high, usually with a freeze-all plan.

Also known as: trigger shot, HCG trigger, final maturation

Related Canada guides

The IVF trigger injection: timing, hCG and GnRH agonist triggers

Sources

Canadian Fertility and Andrology Society (CFAS)

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

Related terms

hCG (human chorionic gonadotropin)

The pregnancy hormone, also used as a trigger injection.

Agonist trigger

A GnRH agonist used instead of hCG to mature eggs and cut OHSS risk.

Egg retrieval

The procedure that collects eggs from the ovaries with an ultrasound-guided needle.

OHSS (ovarian hyperstimulation syndrome)

An excessive response to fertility drugs that makes the ovaries swell and fluid shift.

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