IUI, Medications

The IUI Trigger Shot Explained

Laura Morrissey, RN, BSN

3 min read

What is the trigger shot?

The Trigger Shot goes by that name because it triggers the final maturation of the egg(s) to prepare them for fertilization. The main trigger shot used during IUI cycles is made up of a hormone called hCG or Human Chorionic Gonadotropin.

An hCG trigger shot is most often administered subcutaneously during IUI and timed intercourse cycles, but it can also be administered through an intramuscular injection. Make sure to pay close attention to the instructions provided by your clinic to determine which route you will use to administer your medication. 

Common doses are 10,000 units, 5,000 units, 2,500 units, and 1,000 units. 

Although unlikely to happen in IUI cycles, patients with high egg numbers or high estrogen levels are not candidates for hCG trigger shots due to the risk of ovarian hyperstimulation syndrome or OHSS. According to Mayo Clinic, “Ovarian blood vessels react abnormally to HCG and begin to leak fluid. This fluid swells the ovaries, and sometimes large amounts move into the abdomen.”

How does the trigger shot work?

The hCG trigger shot is used to begin the final maturation of the eggs that you’ve been working so hard to grow during the ovarian stimulation. The trigger shot mimics the action of a hormone known as LH, or Luteinizing Hormone, which your body naturally produces during your menstrual cycle. LH signals the eggs to finish a cell division process called meiosis. Meiosis is when the eggs go from having 46 chromosomes like all other cells in the body to half the genetic material, or 23 chromosomes. 

Meiosis is important because sperm cells also contain only 23 chromosomes. So, when the sperm fertilizes the egg, the two sets of 23 chromosomes combine to make a full 46 chromosomes in the resulting cells of the embryo.

The other key thing that the trigger shot does is to have the maturing egg(s) release from the wall of the follicle. As eggs develop during ovarian stimulation, the immature eggs are attached to the wall of the follicle. When the eggs are mature, the trigger shot causes the eggs to release from the wall of the follicle and into the fluid within the follicle. Shortly thereafter, the egg will be released into the fallopian tube where it can be fertilized by the sperm placed in the uterus during the IUI. 

When is the trigger shot usually done?

The trigger shot is typically administered around 24 to 36 hours before your IUI procedure. Your clinic will likely provide you with specific instructions and timing that coincides with your IUI procedure.

What happens if the timing isn’t right?

  • If you were to try to do an IUI too soon after the trigger shot, the egg(s) may not have completed the process of meiosis or may not have been released into the fallopian tube, making for poor timing for fertilization after the IUI.

  • If you did the IUI too long after the trigger shot, the egg(s) will no longer be viable and able to be fertilized by the sperm inserted during the IUI. 

How do I prepare for the trigger shot?

The first and most important step for the trigger shot is to check a few days ahead of time that you have everything you need to complete the shot. Make sure you have the medication and all of the supplies:

  • Trigger medication

  • Correct injection needle 

  • Correct syringe

You can confirm the plans for what type of trigger shot and what supplies you’ll need with your clinic in advance to be sure everything is ready to go on the day of the trigger shot. 

The trigger shot can be a stressful time during your cycle. It’s exciting to prepare for the IUI and the chance to get pregnant, but there’s also a lot riding on this one injection. Just remember, you’ve accomplished so much this cycle already and you’re almost to the finish line!  

Need help with your trigger shots? Check out our articles all about how to do your injections to make sure you’re comfortable with the process before getting started! 

Fertility Medications: Pro Tips For How To Do a Subcutaneous Injection

How to Do Intramuscular Injections Like a Pro