What’s a Trigger Shot and How Does It Work?

Medically reviewed by Linda Streety, RN, BSN

You’re looking at your IVF protocol, checking out what’s ahead of you this month, and you spot this term: trigger shot. What is it and why does it matter?

6 Second Snapshot

  • When your eggs have developed to the right size, your doctor will schedule your trigger shot.
  • The trigger shot is a hormonal shot that “triggers” your eggs to mature so they can be captured by an egg retrieval procedure.
  • The trigger shot will likely be either hcG, leuprolide acetate (Lupron), or both, depending on the IVF stimulation protocol your doctor chose for you.

What is a trigger shot?

At the beginning of your IVF cycle, hormones are carefully administered so your body prepares more eggs than usual in a process called ovarian stimulation. The trigger shot helps doctors control when those eggs mature so they can be captured by an egg retrieval procedure. Depending on the IVF stimulation protocol your doctor chose for you, your trigger shot medication will be either hCG or Lupron or a combination of the two.

Human chorionic gonadotropin (hCG): This hormone is produced in the placenta during early pregnancy. It can also be used during IVF. When you administer hCG as a trigger shot, it stimulates the eggs to mature because hCG is very similar to LH (luteinizing hormone) which causes ovulation. Your doctor may use hCG as the trigger during a long agonist, antagonist, or flare protocol.

Lupron (leuprolide acetate): Your doctor may choose this trigger shot medication to set off the surge of LH hormone needed to mature your eggs during an antagonist protocol.

The antagonist protocol with a Lupron shot is frequently chosen because it lowers the risk of Ovarian Hyperstimulation Syndrome, or OHSS. During the early part of your IVF cycle, your doctor will monitor you carefully for signs of OHSS. This relatively rare complication can result in uncomfortable abdominal bloating and pain. While OHSS usually resolves on its own, it can lead to ovarian torsion, in which the ovary twists. This causes intense pain in the pelvis and could cut off blood flow to the ovary. While the ovary can sometimes twist back into place, emergency surgery may be necessary.

If your doctor chose an antagonist protocol for you, it’s possible that they may choose a dual trigger shot, in which both Lupron and hCG are used as the trigger.

When do I administer the trigger shot?

Throughout your IVF cycle, your doctor will monitor how large your follicles are through ultrasound imaging. They will also take blood tests to measure your hormone levels as a gauge of your response to the drugs. When your follicles reach the right size, your doctor will schedule the trigger shot so it occurs roughly 36 hours before your egg retrieval. This gives the eggs time to mature and allows for egg retrieval before ovulation.

Your doctor may administer the shot, but most often it can be done at home. The shot can go into your fat tissue or your muscle. While you only need to do it once, it’s important to do it at the exact time your doctor recommends.

After the trigger shot, your eggs will undergo a process called meiosis, when they shed half their chromosomes. Instead of 46 chromosomes, they will now have 23. Upon each egg’s fertilization, its 23 chromosomes combine with 23 chromosomes from the sperm to create an embryo.

What trigger shot side effects can I expect?

The trigger shot may cause some mild irritation at the injection site. Common side effects include bloating and mild pelvic pain. If you develop severe pain, nausea, a tender and tight abdomen, difficulty breathing, or rapid bloating during this time, this could be a sign of OHSS and you should contact your doctor immediately.

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