The trigger shot (hCG or GnRH agonist)

The trigger shot is a single, carefully timed injection given near the end of an IUI or IVF cycle. After several days of medicines growing the follicles, the trigger gives the final signal that matures the eggs inside them and sets the clock for their release, usually about 36 hours later.

Why the timing matters

Everything after the trigger is scheduled from it. In IVF, egg retrieval is planned for just before the eggs would be released naturally. In IUI, the insemination is timed to the same window. A few hours out can matter, so clinics are specific about the exact time to give the injection, sometimes late in the evening.

The two kinds

The common trigger is hCG (sold as brands such as Ovitrelle or Pregnyl), which mimics the body's natural LH surge. In some IVF cycles a clinic uses a GnRH agonist trigger instead, which prompts the body to produce its own surge. The agonist option is often chosen to lower the risk of OHSS, usually where the plan is to freeze the embryos and transfer them in a later cycle.

What to expect

The trigger is a small injection, and side effects are few: some mild bloating or tenderness at the site. One practical point matters. Because hCG is the same hormone a pregnancy test looks for, testing too soon after an hCG trigger can show a false positive from the injection rather than a pregnancy. Wait for the test date your clinic gives you.

The trigger shot in India

It is a standard, routine part of a stimulated cycle, and modest in cost next to the injections that come before it. It is used within registered ART clinics, which you can look up in our directory.