GnRH agonists and antagonists in IVF

During IVF, the ovaries are stimulated to grow several eggs at once. Left to itself, the body may try to release those eggs too early, before they can be collected. GnRH agonists and antagonists are the drugs that prevent this early release, so that egg retrieval can be timed properly. They are part of the background machinery of an IVF cycle rather than the star of it, but they are what keeps the cycle on schedule.

The two approaches

Most IVF cycles use one of two protocols, named after which of these drugs they use.

In the antagonist protocol, a drug such as cetrorelix or ganirelix is started partway through the stimulation phase and blocks an early surge quickly. It makes for a shorter, more flexible cycle and a lower risk of OHSS, and it is now a common choice for many patients.

In the agonist (long) protocol, a drug such as leuprolide is started earlier and first quietens the body's own hormones, a step called down-regulation, before ovarian stimulation begins. It gives tight control and suits certain situations, at the cost of a longer cycle.

A second role as the trigger

The same agonist drugs have a second use: in an antagonist cycle they can serve as the trigger shot that finishes egg maturation. This choice lowers the risk of OHSS and is often paired with freezing the embryos for a later transfer.

What to expect

These drugs are given as injections or, for some, a nasal spray. Side effects are usually short-lived and hormonal, such as hot flushes or headaches, and tend to be more noticeable with the longer agonist protocol.

Which one is right for you

The protocol is chosen by your clinic from your age, your egg reserve, and your history, and neither is universally better. It is reasonable to ask why a particular protocol was picked for you. These medicines are used within Level 2 registered ART clinics, which you can look up in our directory.