Trigger Shot (hCG / Ovidrel)

What Is a Trigger Shot (hCG / Ovidrel)?

A trigger shot is an injection of synthetic human chorionic gonadotropin (hCG) or a similar hormone that mimics the body’s natural luteinizing hormone (LH) surge, signaling the final maturation and release (ovulation) of eggs from the ovaries. Trigger shots—most commonly given as brand-name drugs like Ovidrel, Pregnyl, or Novarel—are a key step in fertility treatments such as in vitro fertilization (IVF) and intrauterine insemination (IUI).

When used in a fertility cycle, the trigger shot precisely schedules ovulation so that egg retrieval or insemination can be optimally timed for maximum pregnancy chances. Sometimes, gonadotropin-releasing hormone (GnRH) agonists—like Lupron—may be used instead for certain protocols, referred to as a "Lupron trigger" or a "dual trigger" when combined with hCG.

Key Takeaways

The trigger shot is an injectable medication used to induce ovulation in fertility treatments.
It commonly uses hCG (human chorionic gonadotropin) and brand-name drugs include Ovidrel, Pregnyl, and Novarel.
The trigger shot signals the ovaries to begin the final process of egg maturation and ovulation.
Lupron trigger and dual trigger protocols may be used in select cycles.
Precise timing is critical: ovulation typically occurs about 36–40 hours after the trigger shot.
The shot is often used before IUI or IVF egg retrieval to optimize success.
Side effects are usually mild but can include injection site pain, bloating, and rarely ovarian hyperstimulation.
Not everyone undergoing fertility treatment will require or be prescribed a trigger shot.
The type of trigger used may vary based on the treatment protocol and individual medical factors.
Always follow clinic instructions for administration, timing, and next steps after a trigger shot.

What Does "Trigger Shot" Mean in Fertility and Reproductive Health?
How Does the Trigger Shot Work?
Why Is a Trigger Shot Important When Trying to Conceive?
Trigger Shot Types: hCG, Ovidrel, Pregnyl, Novarel, Lupron, and Dual Trigger
When Is the Trigger Shot Timed?
Trigger Shot Quick Facts Table
Risks, Side Effects, and Safety
Common Myths About the Trigger Shot
Who Needs a Trigger Shot, and Who Might Not?
What Happens After the Trigger Shot?
When to See a Fertility Specialist About Trigger Shots
Frequently Asked Questions About Trigger Shots
References and Further Reading
Disclaimer

What Does "Trigger Shot" Mean in Fertility and Reproductive Health?

The trigger shot is a term used in fertility care to describe an injection—usually of the hormone hCG—that induces final maturation and ovulation of eggs from the ovaries. The trigger shot is also sometimes referred to specifically by its medication brand, such as Ovidrel, Pregnyl, or Novarel. In certain cycles, a GnRH agonist like Lupron may be used instead ("Lupron trigger"), or occasionally both drugs are combined ("dual trigger").

The shot mimics the body’s natural LH surge, which is the hormonal cue for ovulation.
In fertility treatment, doctors use the trigger shot to manage the timing of ovulation for procedures like IUI or egg retrieval in IVF.

Key Point: The trigger shot's main role is to ensure that egg release happens at a predictable time, making fertility treatments more effective and easier to schedule.

The phrase "hCG trigger shot" simply refers to a trigger using human chorionic gonadotropin, which binds to LH receptors and acts similarly to the natural hormone. Other protocols may use a GnRH agonist or even a combination, depending on patient risk for side effects such as ovarian hyperstimulation syndrome (OHSS).

How Does the Trigger Shot Work?

The trigger shot initiates the final stages of egg maturation and sets the clock for ovulation.

The Science Behind the Trigger Shot

hCG is structurally similar to LH, so it binds the same receptors and causes the ovary to finish growing its leading follicles and release mature eggs.
Natural ovulation happens 36–40 hours after the LH surge; the trigger shot aims to exactly reproduce this interval.
In IVF, the shot “primes” the eggs just before retrieval; in IUI, it ensures eggs are released for sperm to meet them at the right moment.

What’s Actually Happening?

Follicles are monitored using ultrasound and hormone levels until they reach optimal size (usually 16–20 mm).
When follicles are ready, the clinic instructs the person to self-inject (or receive) the trigger shot.
Ovulation is set in motion: within about 36 hours, eggs are released (IUI), or are ready for retrieval (IVF).

Types of Trigger Shots

hCG: Ovidrel (in pre-filled syringe, subcutaneous injection), Pregnyl and Novarel (administered intramuscularly or subcutaneously).
GnRH agonists: Lupron is sometimes used for people at high risk of ovarian hyperstimulation.
Dual trigger: Combination of hCG and GnRH agonist to maximize egg maturation and reduce risk.

Why Is a Trigger Shot Important When Trying to Conceive?

The trigger shot is crucial in assisted reproductive technology for several reasons:

Precise Timing: Allows doctors or people trying to conceive to perfectly synchronize IUI or IVF with ovulation, optimizing the chances of fertilization.
Reduces Missed Windows: Natural ovulation can be unpredictable. Scheduling a trigger shot ensures eggs aren't released too early or too late.
Egg Maturity: Ensures eggs have completed maturation, which may improve fertilization and embryo quality.
Cycle Coordination: Especially critical for donor cycles, shared cycles, egg freezing, and gestational surrogacy, where timing must be exact for all parties.

Did you know? About 90% of IVF cycles and a large percentage of medicated IUI cycles use some form of a trigger shot.source

Trigger Shot Types: hCG, Ovidrel, Pregnyl, Novarel, Lupron, and Dual Trigger

hCG Trigger (Ovidrel, Pregnyl, Novarel)

Ovidrel: Pre-filled syringe, subcutaneous.
Pregnyl/Novarel: Powder form mixed with liquid, intramuscular or subcutaneous.
Function the same way as LH, initiating final egg maturation.

Lupron Trigger

Lupron (leuprolide acetate): A GnRH agonist, used particularly for people at risk of OHSS or with certain hormonal profiles.
May reduce risk of ovarian hyperstimulation, but may require adjusted luteal support after.

Dual Trigger

Combo of hCG plus GnRH agonist (like Lupron).
Sometimes used to improve both egg maturation and reduce hyperstimulation risk.

Key Point: The exact choice of trigger shot depends on the protocol, individual health, and prior cycle outcomes. Always follow your clinic’s recommendation.

When Is the Trigger Shot Timed?

The timing of the trigger shot is critical and is based on imaging and hormone monitoring.

The trigger is usually given when the leading follicle(s) reach a specific size (often 18–20 mm).
Ovulation or optimal egg maturity occurs about 36–40 hours after the injection.
For IUI cycles: The insemination is typically scheduled 24–36 hours after the trigger.
For IVF cycles: Egg retrieval is scheduled 34–36 hours after the trigger to retrieve eggs before spontaneous ovulation.
Timing matters! Delays or early administration can lead to cycle cancellation or empty follicles during retrieval.

Example Timeline Table

Cycle Type	Trigger Shot Given	Procedure Timing
IUI	Cycle Day 12 p.m.	IUI on Day 14 morning
IVF Retrieval	Cycle Day 12 8 p.m.	Retrieval on Day 14 at 8 a.m.

Trigger Shot Quick Facts Table

Attribute	Details
Drug names	Ovidrel, Pregnyl, Novarel, Lupron
Hormone used	hCG (most common), or GnRH agonist (Lupron)
Injection type	Subcutaneous (Ovidrel, Lupron); Intramuscular (Pregnyl, Novarel)
Used in	IVF, IUI, ovulation induction, egg freezing, donor cycles
Purpose	Induce final egg maturation and schedule ovulation
Timing to ovulation/egg retrieval	36–40 hours (ovulation); 34–36 hours (retrieval)
Common side effects	Bloating, cramps, injection site pain, rare allergic reaction
Main risks	Ovarian hyperstimulation syndrome (OHSS, especially with hCG)
Not used in	Unmonitored cycles, natural conception without monitoring

Risks, Side Effects, and Safety

While the trigger shot is generally safe and well-tolerated, it can have side effects and risks.

Common Side Effects

Mild abdominal discomfort or bloating
Breast tenderness
Injection site reactions (bruising, redness, stinging)
Mild headache or fatigue
Rarely, allergic reaction

Rare but Serious Risks

Ovarian Hyperstimulation Syndrome (OHSS): Especially with hCG triggers and in people with many follicles. Can cause severe bloating, shortness of breath, rapid weight gain, and abdominal pain.OHSS resource
Human error in injection timing can compromise cycle outcomes.

Did you know? Clinics may switch from hCG to a Lupron trigger for people at risk for OHSS to reduce this complication.

Safety Tips

Always follow your clinic's instructions carefully regarding mixing, dosing, and timing.
Monitor for severe abdominal pain, rapid weight gain, or breathing difficulties—these require urgent medical attention.
Discuss prior allergic reactions to similar medications with your care team.

Common Myths About the Trigger Shot

Here is a table contrasting some prevalent myths with facts:

Myth	Fact
The trigger shot guarantees ovulation for everyone	While very effective, some cycles can result in failed ovulation or empty follicles
hCG trigger shots are dangerous for everyone	Most people tolerate them well; risk for OHSS is mostly in high responders
Timing doesn't matter as long as you take the shot on the right cycle day	The exact clock is critical; even a few hours' deviation can impact outcomes
The trigger shot can harm an early pregnancy	The shot is used before conception; it doesn't affect established pregnancies
All trigger shots involve hCG	Lupron trigger and dual triggers use alternate or combined hormones
Home pregnancy tests are reliable right after a trigger shot	hCG in the trigger shot can cause false-positive pregnancy tests for up to 10–14 days

Who Needs a Trigger Shot, and Who Might Not?

Who Typically Needs a Trigger Shot

People undergoing monitored ovulation induction (with Clomid, letrozole, or injections)
IUI (intrauterine insemination) cycles
IVF egg retrieval cycles
Donor egg cycles, egg freezing cycles, embryo banking

Who Might Not Need One

People with regular, reliably timed ovulation and no evidence of ovulatory disorder
Some natural IUI cycles where ovulation is tracked with LH kits alone
IVF cycles using "natural" (no stimulation) or "modified natural" approaches

Key Point: The decision to use a trigger shot is individualized after monitoring and discussion with your clinic.

What Happens After the Trigger Shot?

IUI Cycles

People with ovaries will ovulate about 36 hours after the shot.
The IUI is strategically scheduled so that sperm are present in the reproductive tract when the eggs are released.

IVF Cycles

Eggs finish maturing and are collected via a minor surgical procedure (egg retrieval) approximately 34–36 hours after the injection.
Not following the timing plan may lead to missed or unfertilizable eggs.

After Either Procedure

Most people can return to normal activities after the injection.
Monitoring for OHSS symptoms is critical in high-responder cycles, especially after trigger shots with hCG.

When to See a Fertility Specialist About Trigger Shots

You’re undergoing or considering IUI or IVF and want to understand protocol options.
You have a history of failed ovulation induction or "no eggs" retrieved in a prior cycle.
You have concerns about risk for OHSS (polycystic ovary syndrome/PCOS, high antral follicle count, previous adrenal/hormonal issues).
You experience severe side effects or possible signs of OHSS after the shot.

Did you know? Fertility clinics often provide precise, hour-by-hour instructions and may offer in-person or telemedicine support for trigger shot administration.

Frequently Asked Questions About Trigger Shots

What does a trigger shot do in a fertility cycle?

A trigger shot induces final egg maturation and initiates ovulation for precise scheduling in fertility treatments.

The hormone in the trigger shot (usually hCG) mimics the body’s luteinizing hormone (LH), causing the ovaries to release mature eggs within about 36–40 hours. This allows insemination (IUI) or egg retrieval (IVF) to be timed for optimal conception chances.

What is the difference between hCG trigger shot, Lupron trigger, and dual trigger?

An hCG trigger uses synthetic human chorionic gonadotropin, a Lupron trigger uses a GnRH agonist, and a dual trigger combines both.

The hCG trigger is standard and effective for most, but a Lupron trigger may be used for people at high risk of OHSS. The dual trigger approach sometimes helps maximize mature eggs and reduce side effects, depending on the case.hCG vs. GnRH agonist study

When should the trigger shot be administered in a typical cycle?

The trigger shot is given when the leading ovarian follicle(s) reach a specified size (often 18–20 mm), after which ovulation or egg retrieval is planned.

This is usually determined via ultrasound and blood tests by your fertility clinic. Never take a trigger shot without clinical monitoring if you are undergoing ART procedures.

How soon after the trigger shot does ovulation occur?

Ovulation typically occurs about 36–40 hours after the trigger shot.

For IUI, insemination is planned for about 24–36 hours post-injection; for IVF, egg retrieval aims for 34–36 hours to collect eggs before their release.timing source

Can you ovulate late or early after a trigger shot?

Most people ovulate on a predictable schedule, but rarely, natural ovulation may occur earlier, or ovulation may be delayed, especially if not all follicles respond.

Accurate timing, close monitoring, and adherence to your clinic's instructions help reduce these risks. If cycles are unpredictable, the protocol may be adjusted next time.

What are the side effects of a trigger shot?

Common side effects include mild bloating, cramps, breast tenderness, or injection site soreness.

Rarely, there can be allergic reactions, worsening of OHSS, or (very rarely) more serious complications. Report symptoms like severe bloating, chest pain, or shortness of breath to your doctor immediately.

Can a trigger shot cause ovarian hyperstimulation syndrome (OHSS)?

Yes, especially in those with high follicle counts or certain hormone profiles; hCG-based triggers increase OHSS risk more than GnRH agonist triggers.

People with PCOS and high estradiol levels are more susceptible. Your clinic may switch to a Lupron or dual trigger if you are high-risk.OHSS prevention article

Does a trigger shot guarantee that ovulation will happen?

The trigger shot is highly effective, but there can still be rare cases of failed ovulation or egg maturation.

This can occur if the follicles are not fully developed, if there is a technical problem with administration, or if there are underlying ovarian or hormonal factors. Clinics will adjust timing and protocol if this occurs.failure rates source

Can I do a trigger shot at home by myself?

Yes, most clinics teach people to self-administer the injection at home.

You may receive in-person training or follow video/printed instructions. If you have needle anxiety or concerns, call your fertility team for support.

Will the trigger shot affect the results of my home pregnancy test?

Yes, hCG from the trigger shot can linger in the body for up to 10–14 days, causing potential false-positive results on pregnancy tests.

Most experts recommend waiting at least 10–14 days after your trigger shot before testing, or confirming results with a doctor’s office blood test.

How is Ovidrel different from Pregnyl or Novarel?

Ovidrel is a recombinant (synthetic) hCG given subcutaneously, while Pregnyl and Novarel are urinary-derived hCG preparations and can be administered via intramuscular or subcutaneous injection.

All act on the same pathway; differences relate to form, purity, and route of administration. Your clinic will choose the most appropriate option for your protocol.

Who shouldn't use a trigger shot?

People with certain hormone sensitivities, allergies, or who are at extremely high risk for OHSS may not be eligible for hCG triggers.

Alternative protocols (Lupron or natural triggers) may be used. Always share your complete medical history with your fertility clinician.

Is a trigger shot painful?

Most people report only mild discomfort from the injection.

Side effects are usually limited to localized pain or bruising at the injection site, which typically resolves within a day.

How much does a trigger shot cost, and is it covered by insurance?

Costs vary from $80 to $250 per injection, depending on type and pharmacy, and may be included in your fertility treatment package.

Insurance coverage is highly variable; check with your provider and pharmacy. Some fertility grants and programs may help with medication costs.

Can lifestyle changes influence the effectiveness of the trigger shot?

No lifestyle factors are known to directly affect how well the trigger shot works, but overall ovarian responsiveness can be improved by maintaining a balanced diet, healthy weight, and avoiding smoking.

Adherence to protocol and open communication with your clinic are the biggest predictors of effective cycles.

What should I do if I miss my trigger shot or take it at the wrong time?

Contact your fertility clinic immediately for guidance.

Timing is crucial, and a missed or mistimed shot could compromise cycle success. Clinics may be able to adjust procedures or, in some cases, reschedule your cycle.

When should I see a doctor about side effects after a trigger shot?

Call your clinic promptly if you have severe abdominal pain, rapid weight gain, breathing difficulties, or chest pain after the shot.

These may be signs of OHSS or other complications and should not be ignored. Most mild symptoms (mild cramps, swelling) resolve within a few days.

References and Further Reading

Fauser BCJM, Devroey P, Macklon NS. Multiple ovarian stimulation for IVF: Time for individualized patient protocols. https://pubmed.ncbi.nlm.nih.gov/22269723/
Fatemi HM, Popovic-Todorovic B. GnRH agonist versus hCG for oocyte triggering in ART: A review. https://pubmed.ncbi.nlm.nih.gov/23337755/
Humaidan P, Kol S, Papanikolaou EG. OHSS prevention strategies. https://pubmed.ncbi.nlm.nih.gov/30795931/
Humaidan P, Polyzos NP, Alsbjerg B, et al. The luteal phase after trigger with hCG or GnRH agonist. https://pubmed.ncbi.nlm.nih.gov/25368422/
Delvigne A, Rozenberg S. Review: Epidemiology and prevention of ovarian hyperstimulation syndrome. https://pubmed.ncbi.nlm.nih.gov/21457913/
Seyhan A, Ata B, Uncu G, et al. Natural cycle IVF: A mini review. https://pubmed.ncbi.nlm.nih.gov/27188792/
ASRM. Patient fact sheet: Ovarian Hyperstimulation Syndrome (OHSS) https://www.asrm.org/globalassets/asrm/asrm-content/news-and-publications/patient-fact-sheets-and-booklets/fact-sheets/ovarian_hyperstimulation_syndrome_fact_sheet.pdf
American Society for Reproductive Medicine (ASRM): https://www.asrm.org/
RESOLVE: The National Infertility Association. https://resolve.org/infertility-101/fertility-treatments/

Disclaimer

This article is for informational and educational purposes only and does not constitute medical or mental health advice. It is not a substitute for speaking with a qualified healthcare provider, licensed therapist, or other professional who can consider your individual situation.