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Fertility Glossary

Antagonist protocol

The most common IVF protocol, using a GnRH antagonist to prevent early ovulation.

Medicines & protocols

Stimulation begins near the start of the cycle and an antagonist injection is added after several days to block a premature LH surge. It is shorter than a long agonist protocol and allows an agonist trigger, which greatly reduces the risk of severe OHSS.

Also known as: short protocol, GnRH antagonist protocol

Related Canada guides

Sources

  • Canadian Fertility and Andrology Society (CFAS)
  • ESHRE guidance (used where Canadian wording is unavailable)

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

GnRH antagonist

An injection that immediately blocks a premature LH surge.

Agonist trigger

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

Long agonist protocol

An older IVF protocol that suppresses the pituitary before stimulation begins.

OHSS (ovarian hyperstimulation syndrome)

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

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