The IVF trigger shot is the final injection of ovarian stimulation, timed 34–36 hours before egg retrieval, and it tells your ovaries to finish maturing the eggs. The clock is everything: injected too early, the eggs may not be mature; too late, and you may ovulate before the procedure.
This guide explains how hCG, Lupron (leuprolide) and dual triggers differ, what to do hour by hour around the injection, and how to handle a missed or late dose. Figures follow the American Society for Reproductive Medicine (ASRM) practice guidance, the European Society of Human Reproduction and Embryology (ESHRE) ovarian stimulation guideline, the UK National Health Service (NHS) and peer-reviewed studies, compiled by the ProIVF Medical Editorial Team and reviewed by the ProIVF Medical Advisory Board.
What Is the IVF Trigger Shot?
The trigger shot is a single injection — either human chorionic gonadotropin (hCG) or a GnRH agonist such as leuprolide (Lupron) — that mimics the body’s natural LH surge. In an IVF cycle, stimulation medications suppress that surge, so the clinic replaces it artificially.
In a natural cycle, a surge of luteinizing hormone (LH) from the brain releases a mature egg about 36 hours later. The trigger shot does the same job on command:
- It completes meiosis (the final maturation division) in each egg, making it ready for fertilization.
- It loosens eggs from the follicle wall so they can be aspirated at retrieval.
- It starts the luteal-phase changes that matter for a fresh embryo transfer.
Without a trigger, most retrieved eggs stay immature, and the number of usable eggs drops sharply.
When Do You Take the Trigger Shot?
Clinics schedule the trigger only when ultrasound shows the leading follicles at 18–22 mm and estradiol (E2) levels indicate good follicle quality, in line with ASRM practice guidance and the ESHRE ovarian stimulation guideline.
Retrieval is then booked exactly 34–36 hours after the injection. Because retrieval is usually early morning, the injection typically happens around 9–10 PM the previous night — which is why many patients call it the “night shot.”
| Event | Typical timing |
|---|---|
| Last follicle check (ultrasound + blood test) | Morning of the trigger decision day |
| Trigger injection | That evening, often 9–10 PM |
| Egg retrieval | 34–36 hours after the trigger (e.g., 9 PM injection → 7–9 AM retrieval two mornings later) |
| Fresh embryo transfer (if applicable) | 3–5 days after retrieval |
The 34–36 hour window is fixed together with your retrieval appointment and should not be moved on your own. If you miss your injection time by more than an hour or two, call the clinic immediately rather than deciding to inject later.
hCG, Lupron or Dual Trigger: Which One Fits You?
Three trigger strategies are used in modern IVF, and the right one depends on your OHSS risk, follicle count and transfer plan.
hCG Trigger — Ovidrel, Pregnyl, Novarel
hCG is the classic trigger. It binds the same receptor as LH but stays active far longer, producing a sustained, powerful maturation signal.
| Brand | Type | Typical dose | Notes |
|---|---|---|---|
| Ovidrel | Recombinant hCG | 250 mcg (prefilled pen) | Most common; subcutaneous injection |
| Pregnyl | Urinary hCG | 5,000–10,000 IU | Intramuscular injection |
| Novarel | Urinary hCG | 5,000–10,000 IU | Intramuscular injection |
Pros: reliable egg maturation and strong luteal-phase support, which helps a fresh transfer. Cons: hCG lingers in the blood for days, which can cause a false positive on a home pregnancy test, and it raises OHSS risk in susceptible patients. For the full list of drugs used in a cycle, see our IVF medications guide.
GnRH Agonist Trigger with Lupron
A Lupron trigger uses leuprolide (often a small dose such as 0.5–1 mg) to make your own pituitary release a shorter, more natural LH surge. Its biggest advantage is a much lower OHSS risk, which is why it is the standard choice for high-risk patients — women with polycystic ovary syndrome (PCOS), many follicles or very high estradiol.
The trade-off is a shorter luteal phase: without extra support, pregnancy rates after a fresh transfer fall, so clinics usually intensify luteal support (estrogen plus progesterone) or move to a frozen transfer plan.
Dual Trigger — hCG + GnRH Agonist
A dual trigger combines a reduced hCG dose with a GnRH agonist, aiming for hCG’s maturation reliability plus the agonist’s OHSS safety. Evidence on whether it improves outcomes is still mixed.
A randomized trial in advanced-maternal-age patients found no significant difference in mature egg yield between hCG alone and dual trigger — Journal of Ovarian Research, 2026. A randomized trial in antagonist cycles also found no significant improvement in most outcomes, though the risk of moderate OHSS was lower — JBRA Assisted Reproduction, 2023.
In practice, the dual trigger is not a universal upgrade — it suits selected high-risk or poor-responder cases, and the choice should follow your follicle count, estradiol level, OHSS risk and fresh-versus-frozen plan.
| Feature | hCG | Lupron (GnRHa) | Dual trigger |
|---|---|---|---|
| Egg maturation reliability | High (gold standard) | Good | High |
| OHSS risk | Higher | Much lower | Intermediate |
| Fresh transfer support | Strong luteal phase | Needs extra support | Intermediate |
| Common for | Standard-risk patients | High OHSS risk (PCOS, high E2) | Selected high-risk or poor-responder cases |
What Happens After the Trigger Shot?
In the 34–36 hours after the injection, the eggs inside each follicle complete their final maturation division. Mild bloating, pelvic pressure or light spotting in this window is normal, and most patients keep up light daily activity — no bed rest is needed.
On retrieval day, the doctor aspirates fluid from each follicle through a thin, ultrasound-guided needle while the embryologist searches it for mature eggs. The procedure takes about 15–30 minutes under sedation; our egg retrieval guide walks through the full day.
What Are the Side Effects and Risks?
Most trigger-shot side effects are mild and short-lived. The one serious risk is ovarian hyperstimulation syndrome (OHSS), mainly after an hCG trigger in high-risk patients.
- Injection-site pain — redness or a small lump that fades within 1–2 days.
- Bloating and pelvic pressure — from enlarged ovaries; usually worst around retrieval.
- Mood swings or fatigue — the hormonal swing can flatten your energy for a few days.
- False positive pregnancy test — trigger hCG can still be detected 7–14 days later; rely on the clinic’s official beta-hCG blood date.
“Ovarian hyperstimulation syndrome (OHSS) is an exaggerated response to excess hormones.” — American Society for Reproductive Medicine, ASRM, Ovarian Hyperstimulation Syndrome patient FAQ, cited 2026
OHSS warning signs are rapid weight gain, severe abdominal pain, nausea and vomiting, and reduced urination — contact your clinic or emergency care immediately if they appear. If you have PCOS, a high follicle count, high estradiol, or you are young and slim, confirm your OHSS risk level and the clinic’s plan before the injection.
What If You Miss or Delay the Trigger Shot?
- Late or missed dose: Call the clinic at once. Depending on the delay, they may move the retrieval time or, in rare cases, cancel the cycle.
- Wrong site or dose: Do not try to correct it yourself; report it and let the clinic decide whether to proceed or adjust.
- Worried you ruined the cycle: The 34–36 hour window carries some tolerance for small deviations, but any error should be reported rather than hidden.
Three Patients, Three Different Trigger Plans
The following stories are shared with consent; names and identifying details have been changed to protect privacy.
Mia, 34, Los Angeles, first cycle — the 9 PM alarm: “My clinic gave me a fixed time — 9:10 PM — with retrieval booked for 7:20 AM two days later. I set three alarms and taped the pen to the fridge door so I couldn’t miss it. My biggest fear was getting the time wrong. The injection itself was a tiny pinch; honestly, the daily stimulation shots were harder. They retrieved 12 eggs, 9 were mature, and we ended up with 2 transferable blastocysts. When the nurse said ‘perfect timing,’ I nearly cried — all that anxiety over one little pen.”
Priya, 38, New York, high OHSS risk — why she got Lupron: “I have PCOS, and my estradiol ran high, so my doctor chose a Lupron trigger instead of hCG. I had read that fresh transfers in Lupron cycles score slightly lower, so I asked her about it. She explained we planned a frozen transfer anyway, and avoiding OHSS mattered more for my safety. I got bloated but never developed OHSS. The frozen transfer about four months later worked on the first try. I’m glad I asked out loud instead of silently worrying.”
Elena, 41, Madrid, second cycle — the false positive scare: “After my first cycle I took a home test too early and saw a faint second line — I was over the moon. The official beta-hCG came back negative and I crashed. My doctor explained the faint line was just leftover trigger hCG, and only the official blood-test date counts. In my second cycle I waited until the blood test. It was negative again, but at least I skipped the false-hope rollercoaster.”
FAQ
Q: How many hours before egg retrieval is the trigger shot given?
The hCG trigger is given 34–36 hours before retrieval. The exact time is locked together with your retrieval appointment; Lupron trigger timing is similar (usually about 36 hours).
Never adjust it on your own.
Q: Does the trigger shot hurt?
Most patients feel only a brief pinch — the trigger is a single injection, and many say the daily stimulation shots were harder. Intramuscular hCG (into the buttock) can sting a little more for 1–2 minutes.
Q: Can the trigger shot cause a false positive pregnancy test?
Yes. hCG from the trigger can stay detectable for 7–14 days, so a home test before the clinic’s official beta-hCG date can show a false positive. A GnRH agonist (Lupron) trigger contains no hCG and does not cause this.
Q: What is the difference between a trigger shot and a booster shot?
A booster is a small additional hCG dose given 2–3 days after the main trigger to support the luteal phase, usually in fresh transfer cycles. The main trigger matures the eggs; the booster maintains progesterone afterward.
Frozen transfer cycles usually need no booster.
Q: Do I need a Lupron trigger if I have PCOS?
Patients with PCOS, many follicles or high estradiol face higher OHSS risk, so clinics commonly choose a Lupron or dual trigger for them — often with a freeze-all plan, meaning transfer happens weeks or months later instead of 3–5 days after retrieval. Your doctor confirms the plan from trigger-day bloodwork and ultrasound.
Q: Can I exercise after the trigger shot?
Light activity is fine. Avoid vigorous exercise, heavy lifting, twisting motions and intercourse between the trigger and retrieval — the ovaries are enlarged and at risk of torsion.
After retrieval, most patients rest 1–2 days before resuming normal activity, following the clinic’s guidance.
Q: What if my injection site is red or swollen?
A small red lump or bruise is common and fades within 1–2 days. Contact the clinic if the area keeps spreading, feels hot, or pain is severe — but this is rare.
Q: How much does the trigger shot cost?
A single hCG trigger (Ovidrel pen) typically costs $100–$200 at US pharmacies; urinary hCG (Pregnyl, Novarel) and Lupron are usually less. That is a small slice of total medication costs, which run roughly $1,500–$6,000 per cycle — NHS IVF overview.
How to Prepare for Your Trigger Shot
- Confirm the exact time and site with your clinic on the day — write it down and set phone alarms.
- Check the medication — brand, dose and expiry before injecting; if anything looks wrong, call the clinic instead of guessing.
- Lock in your retrieval time — it is tied to the injection, so plan travel, time off work and childcare around both. After injecting, log the time, site and how you feel so you can brief the doctor accurately on retrieval day.
- Ask about testing dates — when is the official beta-hCG blood draw, and should you avoid home tests before it?
- Review your OHSS risk — if you have many follicles or high estradiol, ask directly whether a Lupron or dual trigger plus a frozen transfer is the better plan for you.
The trigger shot is one small injection, but it controls the timing of the most important procedure in your cycle. Once you understand why, when and how it works, most of the anxiety disappears — the night before, check your alarm, your medication and your retrieval time together and you will feel settled.
If you are new to IVF, our step-by-step IVF process guide covers every stage from preparation to pregnancy test. To compare how clinics handle trigger choices and retrieval timing, browse our hospital directory or contact us for guidance.
Medical disclaimer: This article is for educational purposes only and does not replace advice from a qualified fertility specialist. Always follow the specific instructions of your clinic.
This article was written by the ProIVF Medical Editorial Team, reviewed by the ProIVF Medical Advisory Board, and is based on publicly available data from ASRM, ESHRE, NHS and peer-reviewed medical literature to provide objective, accurate information for patients.
Last updated: 2026-08-03.
