Medications, IVF, Egg Freezing

IVF and Egg Freezing: The Trigger Shot Explained

Laura Morrissey, RN, BSN

5 min read

What is the trigger shot?

The trigger shot goes by that name because it’s the last injection done in a fertility treatment cycle that triggers the final maturation of the eggs to prepare them for the egg retrieval. There are two types of trigger shots: 

  1. those made up of a hormone called hCG or Human Chorionic Gonadotropin and

  2. those made up of leuprolide acetate, which your provider may refer to as Lupron. 

1. Human chorionic gonadotropin (hCG) Trigger

hCG is very commonly used as a trigger shot. It’s most often administered intramuscularly during IVF and egg freezing cycles but is also prescribed subcutaneously most commonly during IUI and timed intercourse cycles (be sure to pay close attention to your instructions from your clinic!). 

Typically, hCG comes as a vial of powder paired with another vial full of bacteriostatic water. The most commonly prescribed vial contains 10,000 units of hCG. Based on the instructions from your clinic, you may be told to only give yourself a portion of the contents in order to give a lower dose. Your clinic will provide you with specific details about your dose and the proper way to draw up just the right amount that you need.

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

hCG is not typically used as a trigger for patients with high egg numbers or high estrogen levels 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.” 

2. Lupron Trigger

Lupron triggers use leuprolide acetate injections to trigger the final maturation of the eggs to prepare for the egg retrieval. Lupron is administered subcutaneously ( in the fatty layer under the skin) and is usually administered through two injections that take place 12 hours apart.

The dosage of the Lupron trigger will be determined by your doctor. Lupron dosage can be done using units or by volume (ml). So, you may receive a syringe labeled with units like an insulin syringe or you may receive a 1ml syringe.  


When drawing up your Lupron dosage, note that 0.1ml = 10 units, 0.2ml = 20 units, etc. That way, if you’re instructed to inject 10 units of Lupron, but have a syringe labeled with milliliters, you can convert it easily!

A Lupron trigger is not an option for people using Lupron as an agonist to prevent ovulation during their treatment cycle. Those patients can only use an hCG trigger. Lupron triggers are great for patients who are at high risk of OHSS because they don’t have the same side effects that come along with the hCG trigger.

Combination Trigger

Combination triggers use a combination of both hCG and Lupron. The combo trigger may include only one Lupron injection on the night of the hCG trigger or may include two Lupron injections that are 12 hours apart, one at the same time as the hCG trigger shot and one Lupron injection the following morning. Your clinic will confirm your specific trigger times and instructions.

How does the trigger shot work?

Both the hCG and the Lupron triggers are 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 these maturing eggs release themselves 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 and ready to be retrieved, the trigger shot causes the eggs to release from the wall of the follicle and into the fluid within the follicle. This is important because during the egg retrieval, the doctor will insert a needle into each follicle and withdraw all of the fluid. Within the fluid will be the eggs that responded to the trigger shot. The vials of follicular fluid are then passed over to the lab to sort through and find the eggs.

When is the trigger shot usually done?

The timing of the trigger shot is critical! The trigger shot is typically administered around 36 hours before your egg retrieval procedure. Your clinic will provide you with a specific time to do the shot that coincides with your retrieval time. If you’re doing a combo trigger or a Lupron trigger, you’ll do your first trigger shot about 36 hours before your retrieval and then the second Lupron trigger shot 24 hours before the retrieval. 

What happens if the timing isn’t right?

  • If you were to try to do an egg retrieval too soon after the trigger shot, many or all of the eggs may not have completed the process of meiosis or may not have been released into the follicular fluid, making for poor results during the egg retrieval. 

  • If you did the retrieval too long after the trigger shot, the eggs will have ovulated into the fallopian tubes and therefore none of the eggs would be available in the follicular fluid to be retrieved during the procedure.

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 (even better to check before your treatment cycle begins) that you have everything you need to complete the shot. Make sure you have the medication and all of the supplies:

  • Trigger medication(s)

  • 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 that everything is ready to go on the night of the trigger shot. 

Because the trigger shot is precisely timed and is crucial to the success of the cycle, it can bring out a lot of anxiety. The best way to combat the nerves is to lay everything out beforehand. About 15 to 30 minutes before injection time, find a flat surface and take out the needle and syringe you’ll be using and draw up the medication. That way, when injection time approaches, you won’t be rushing to prep everything in time.

The timing of the trigger shot is critical, but keep in mind that injecting a few minutes before or after your instructed injection time is just fine! The important thing is to take your time and be safe administering your injection.

If you missed your trigger time by a large amount of time (think 30 minutes or more) contact your clinic ASAP to let them know and see if they need to adjust your egg retrieval procedure time. 

The trigger shot can be a stressful time during your cycle. It’s exciting to prepare for the retrieval, 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! 

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