Trigger Shots (hCG and GnRH Agonist): What They Do and When

What is a trigger shot?

A trigger shot is an injection that finishes the maturation of eggs and triggers their release. It takes the role of the body’s natural LH surge, and it is given when ultrasound shows that follicles have reached the right size. It lets clinicians time IUI, intercourse or an IVF egg retrieval very precisely.

Types of trigger

• hCG triggers (such as Ovidrel, Pregnyl and Novarel) act like LH and are the most common.
• GnRH agonist triggers (leuprolide, sometimes called a “Lupron trigger”) cause the pituitary to release its own LH and FSH, and may lower the risk of OHSS in IVF cycles for people who respond strongly.
• Dual triggers combine both in some protocols.

Your clinician chooses based on your response and the treatment.

Timing

Ovulation usually occurs about 36 to 40 hours after an hCG trigger. In IVF, retrieval is scheduled around 34 to 36 hours after the injection. Clinics give exact instructions, usually for an evening time. Set an alarm and ask what to do if you miss it.

When it is used

• In IVF and egg freezing after gonadotropin stimulation
• In IUI and ovulation induction cycles to time insemination
• In some timed-intercourse cycles under monitoring

Not every medicated cycle needs a trigger. Some clinics rely on natural LH surges detected with ovulation tests.

Side effects and cautions

• Mild soreness or bruising where you inject
• Bloating or pelvic discomfort
• A false-positive home pregnancy test if you test too soon after hCG. Ask your clinic when to take a reliable test.
• Rarely, ovarian hyperstimulation syndrome (OHSS)

Questions to ask

Which trigger and dose are you recommending and why? What time should I take it? What if I miss the time? When can I take a reliable pregnancy test?

Why timing is so precise

The trigger imitates the LH surge that normally precedes ovulation by about a day and a half. Egg retrieval is scheduled shortly before ovulation would occur, so that mature eggs can be collected before they are released. If the trigger is taken too late, eggs may be released before retrieval. Too early, and eggs may be immature. That is why clinics give a specific time and ask you to set an alarm, and why they may ask you to confirm by text once you have done it.

How the shot is given

Some triggers are given as a small subcutaneous injection in the abdomen, similar to other fertility shots. Others, such as some hCG preparations, are given intramuscularly, usually in the upper buttock, with a longer needle. If you will need an intramuscular injection, ask your nurse to demonstrate, and consider asking your partner to learn. Many people prefer to have it done in the clinic.

Choosing the trigger

Clinicians choose between hCG and GnRH agonist triggers based on your response and risk. People with many follicles are at higher risk for OHSS, and an agonist trigger can lower that risk. In egg donation and freezing cycles, agonist triggers are common for this reason. A dual trigger combines both medicines in some protocols to improve egg maturation. Your clinic will explain its approach.

What if I forget or mistime it?

Call your clinic immediately. Do not wait. Depending on how late it is, they may move the retrieval or IUI, or advise on another plan. Keep the instructions somewhere you can find them, and double check the time zone if you are traveling.

Home pregnancy tests after a trigger

Because hCG triggers can stay in the body for days, a positive result soon after may reflect the injection. Some people take tests every day after a trigger to watch the line fade, which can be stressful. Ask your clinic whether it recommends this, and when to take a test that reflects a true result.

Storage and handling

Some trigger medications must be stored in the refrigerator and brought to room temperature, while others are stable at room temperature. Check the label and ask your pharmacy.

Questions to ask

• Which trigger and dose will I use, and why?
• What exact time should I take it, and what if I miss it?
• Can I have it given at the clinic?
• When should I take a pregnancy test, given the trigger?

Practical checklist for trigger night

Confirm the exact time with your clinic and set two alarms. Check that you have the right medication and supplies, including alcohol swabs and a sharps container. Wash your hands, choose your injection site, and allow the medicine to reach the temperature the label recommends. Take a photo of the clock when you inject, in case the clinic asks. Eat normally, and plan to rest. Keep your clinic’s after-hours number nearby in case anything goes wrong.

After the trigger

If an embryo transfer follows, you will likely start progesterone support. The wait for results can be hard, so see coping with the two-week wait.