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Trigger interpreter calculator

What does my trigger shot mean?

What your trigger type and timing mean, and what to ask before egg collection.

Trigger type

0 hCG, 1 agonist, 2 dual

From your instructions

Lead follicle size

Largest follicle at your last scan

Follicles 11mm or larger

follicles

0 if not measured

These are example numbers. Replace them with yours, then press Calculate.

Example answer

18mm lead follicle

17 to 20mm

The range most units trigger in. The lead follicles are mature and the cohort behind them has usually caught up.

This is a guide, not a diagnosis. Share the result with your doctor.

Your result on the scale

The ranges this calculator uses. Yours is highlighted.

Your numbers

Everything worked out from what you entered.

Trigger type: hCG
What that means: The traditional trigger. Effective, but sustains the stimulus for days and is the main driver of OHSS in high responders.
Lead follicle: 18 mm
Follicle count: Below the 19-follicle threshold usually used to flag OHSS risk.
Egg collection: normally about 36 hours after the trigger

What each result means

Your result is highlighted. Your own clinic's advice always comes first.

Your resultunder 16mm

Earlier than the usual trigger point. Triggering before follicles mature risks collecting immature eggs, so this would be unusual unless there is a specific reason. Worth asking about.

Your result16mm

At the earlier end of the usual window. Some units trigger here, particularly with many follicles developing.

Your result17 to 20mm

The range most units trigger in. The lead follicles are mature and the cohort behind them has usually caught up.

Your resultabove 20mm

Later than the usual window. Waiting can allow follicles to begin luteinising, and in antagonist cycles there is a risk of ovulating before collection. Ask what they are waiting for.

Where this fits in your journey

The usual order, from trying to conceive to pregnancy. Not everyone needs every stage. This calculator belongs to stage 4.

Stage 4 · you are here

During an IVF cycle

Make sense of the numbers your clinic gives you.

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This calculator: What does my trigger shot mean?

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How this is worked out

InterpretationExplains a result or decision you already have. It recommends nothing.

Reads back the trigger your clinic has planned or given, against the pattern normally used. It does not tell you when to trigger — that is decided on the day from follicle measurements this form cannot see.

About this calculator

?What it tells you

Trigger type and timing, and what to ask. What your trigger type and timing mean, and what to ask before egg collection.

✓When to use it

Never — this is your clinician’s decision

iWhat you need

Trigger type (0 hCG, 1 agonist, 2 dual)
Lead follicle size (mm)
Follicles 11mm or larger (follicles)

!What it cannot tell you

This explains a plan you have already been given. Take the trigger at exactly the time your clinic specified — set an alarm for it.

Common questions

Why can trigger timing not be scheduled in advance?

Because it depends on how your follicles grow, which is measured by ultrasound during the cycle. The trigger completes egg maturation and fixes collection about 36 hours later, so it is set on the day rather than at the start.

What is the difference between an hCG and an agonist trigger?

hCG is the traditional choice and sustains the hormonal stimulus for days, which drives OHSS in high responders. A GnRH agonist trigger clears far faster and substantially reduces severe OHSS, which is why it is usually paired with freezing all embryos rather than a fresh transfer.

I have a lot of follicles. Should I ask about anything?

Yes. At 19 or more follicles of 11mm or larger, OHSS risk is recognised as raised. Ask whether an agonist trigger and a freeze-all are being considered, and make sure you have a number to call after collection.

What if I take the trigger at the wrong time?

Call your clinic immediately rather than waiting. Timing determines when eggs are collected and whether they are mature, so they need to know in order to adjust.

What should I ask before my trigger?

What follicle sizes are you waiting for? Will I have hCG or an agonist trigger, and why that one for me? If I am a high responder, would you switch and freeze all embryos?

Sources

Interpretation only. Trigger timing is decided on the day from ultrasound follicle measurements and hormone levels — no form can supply those. Typical practice is to trigger when lead follicles reach roughly 17 to 20mm, read alongside oestradiol and the number of follicles developing. A GnRH agonist trigger with a freeze-all is the most effective prevention of severe OHSS in high responders.

In an emergency

If you have any of the warning signs listed here, don't wait for a test result or a calculator. Get help now.

112All emergencies, anywhere in India 108Ambulance

Also call your IVF clinic. Most clinics give an emergency number on your treatment or discharge sheet. Save it in your phone now, before you need it.