Trigger Shot Explained 2025: Cost, Uses, Side Effects & Success Rates

Embarking on assisted reproductive technology (ART) can feel overwhelming with all the new terminology. One common and crucial element in fertility treatments is the “trigger shot.”

Trigger shots are frequently used alongside timed intercourse, intrauterine insemination (IUI), or in vitro fertilization (IVF). Your healthcare provider will guide you on the correct timing and method of administration in your personalized fertility plan.

Below, we delve into what trigger shots are, how they function, potential side effects, and their impact on treatment outcomes.

What Is a Trigger Shot?

Trigger shots—known by brand names such as Ovidrel, Novarel, or Pregnyl—contain human chorionic gonadotropin (hCG), a hormone similar to the body’s luteinizing hormone (LH). LH naturally surges before ovulation to help eggs mature and release from the ovaries.

Trigger shots fall under gonadotropin therapy, a well-established fertility treatment that stimulates the ovaries, particularly useful for women who do not ovulate regularly, have weak ovulation, or require ovulation control during fertility procedures.

A newer alternative, Lupron, uses a drug agonist to induce an LH surge, reducing the risk of ovarian hyperstimulation syndrome (OHSS) in some patients.

Administered once per cycle, trigger shots can be injected intramuscularly or subcutaneously, with many women opting for a subcutaneous injection in the abdomen.

How Does the Trigger Shot Work?

While follicle-stimulating hormone (FSH) and LH promote egg growth and maturation, the trigger shot’s hCG prompts the ovaries to release mature eggs, synchronizing ovulation for fertility treatments.

Timed Intercourse and IUI

1. Doctors monitor follicle development via ultrasound.
2. Trigger shot is administered as directed.
3. Intercourse or IUI is scheduled approximately 24–36 hours later to coincide with ovulation.

IVF

Before egg retrieval, the trigger shot facilitates meiosis, the critical division reducing egg chromosomes by half to prepare for fertilization. Egg retrieval is then scheduled within 36 hours post-injection, followed by fertilization and embryo transfer.

Who Should Use a Trigger Shot?

Trigger shots are integral to fertility regimens involving timed intercourse, IUI, or IVF. They are combined with other medications and tailored by your doctor based on your unique needs and past responses. Common uses include treating anovulation, unexplained infertility, and enhancing IVF cycles.

Timing the Trigger Shot

Ovulation typically occurs 36 to 40 hours after a trigger shot, making precise timing critical. Your doctor will provide detailed instructions to align the shot with your treatment schedule.

IUI Timing

Trigger shots are given when follicles reach 15–20 mm and the uterine lining is suitably thick (7–8 mm). The IUI procedure follows 24–36 hours post-injection, often accompanied by progesterone supplements to support implantation.

IVF Timing

Follicles are monitored until they reach 15–22 mm, with the shot administered around days 8–12 of your cycle. Egg retrieval occurs within 36 hours, followed by embryo transfer or freezing.

Potential Side Effects

Common side effects include bloating, pelvic discomfort, and injection site soreness. OHSS, a swelling condition of the ovaries, can occur but is rare. Symptoms range from mild (bloating, nausea) to severe (rapid weight gain, breathing difficulties). Immediate medical attention is required for severe cases.

When to Take a Pregnancy Test

Because trigger shots contain hCG, testing too early can cause false positives. It’s recommended to wait at least two weeks post-injection before taking a pregnancy test. Blood tests administered by your doctor provide the most reliable results.

For those eager to monitor hormone levels, daily urine tests can track hCG decline, with fading lines indicating the hormone leaving your system. However, if the line darkens again, pregnancy is likely.

Success Rates of Trigger Shots in Fertility Treatments

Isolating the trigger shot’s success rate is challenging since it’s used with other treatments. However, studies indicate significant improvements in pregnancy rates with trigger shot use. For example, IUI cycles with a trigger shot show pregnancy rates up to 18.2%, compared to 5.8% without. Timing the shot with a natural LH surge can increase rates to over 30%.

Emerging research suggests alternative timing strategies may further improve outcomes, but more studies are needed.

Final Thoughts

Trigger shots are a vital component of modern fertility protocols, enhancing the precision and effectiveness of treatments like IUI and IVF. Consult your fertility specialist to understand how trigger shots fit into your individualized plan and to optimize your chances of conception.

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