Cetrorelix injection in IVF: how it prevents early ovulation
Cetrorelix is a GnRH antagonist injection used in IVF to stop the eggs being released before they can be collected. It is usually added once the lead follicle reaches about 14 mm, given under the skin once every 24 hours alongside the stimulation injection, and continued until the trigger.
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This video is in Hindi; the guide on this page is in English.
Cetrorelix is one of the injections on most IVF plans, and its job is easy to miss: it does not grow eggs, it protects them. In this video, in Hindi, our consultant explains why the injection is needed, opens both the powder form and the ready-filled syringe, shows how the powder is mixed with an insulin syringe, and explains when it is started in the cycle. This guide follows the same points in English; your own plan always comes from your doctor.
Pai Hospital is registered as a Level 2 ART clinic under the Assisted Reproductive Technology (Regulation) Act, 2021 (Reg. No. GA/AC/2022/12689/L2/South Goa/02, valid to 14 January 2030).
Why does IVF need an injection to prevent early ovulation?
IVF stimulation is also called controlled ovarian stimulation: daily injections such as HMG or FSH grow several follicles at the same time, instead of the single follicle of a natural month. Read more about the HMG injection.
As the follicles grow, they make more and more of the hormone estrogen. In a natural cycle, a high estrogen level signals the pituitary gland in the brain to release a burst of LH, called the LH surge, and the egg is released within about a day and a half. During IVF, that surge can come too early, while the follicles are still growing. This is called a premature LH surge. If it happens, the eggs may be released before the planned egg collection, and the cycle may have to be stopped or changed.
In the video, our consultant explains that preventing this premature LH surge is the whole purpose of cetrorelix.
What is a GnRH antagonist?
The pituitary gland releases LH when it is signalled by GnRH (gonadotropin-releasing hormone). Cetrorelix belongs to a group of medicines called GnRH antagonists: it blocks the receptors that GnRH acts on, so the pituitary cannot release a surge of LH. The effect starts within hours and wears off within about a day after the injection is stopped. That is why it is given every day, and why it can be started late in the stimulation. Ganirelix is another medicine of the same group.
The antagonist protocol in IVF
A plan that uses this kind of injection is called the antagonist protocol. It is widely used, because it is short and the antagonist is needed only for the last part of the stimulation:
- The stimulation injections start early in the period, after a baseline scan.
- A scan every one or two days tracks the follicles.
- When the lead follicle crosses about 14 mm, cetrorelix is added as a second daily injection, at a separate site from the stimulation injection.
- Both continue each day until the follicles are mature.
- The trigger injection then completes the maturation of the eggs, and the eggs are collected about a day and a half later.
In the video, our consultant explains that an IVF cycle usually needs about three to five doses, although the number depends on how quickly the follicles mature. Some doctors start the antagonist on a fixed day of stimulation instead of by follicle size; your doctor will tell you which applies to you. The trigger itself, including the dual trigger, is explained in dual trigger in IVF.
An older approach, the long agonist protocol, switches the pituitary off for a couple of weeks before stimulation begins; the antagonist protocol avoids that long lead-in. The day-by-day shape of a whole cycle is set out in the IVF timeline, and every injection used in IVF in IVF injections explained.
The two forms: powder vial and ready-filled syringe
Each pack holds a single dose. In the video, our consultant shows both forms:
- Powder vial with diluent. The powder is mixed with the liquid in the pack, using an insulin syringe, and the whole amount is drawn back and injected under the skin.
- Ready-filled syringe. The medicine is already in the syringe, with a short, fine needle under a cap. Remove the cap and inject under the skin; there is nothing to mix.
The ready-filled form makes it easier to take the injection at home without mixing mistakes, and saves a trip to the hospital each day.
How to take cetrorelix correctly
- The same time every day. The protection lasts about a day, so take each dose within the 24-hour window your doctor gives you.
- Mix carefully. With the powder form, make sure the powder has fully dissolved and that the whole dose is drawn into the syringe.
- Under the skin only. It is given into the fat under the skin of the tummy or the arm, not into the muscle.
- A separate site. Keep it a few centimetres away from where you take the stimulation injection.
- Keep your scan appointments. They decide when the trigger is given and when the injection stops.
Side effects
Cetrorelix is usually well tolerated. The commonest effects are redness, itching or a small swelling where it was injected, which settle on their own. Headache and nausea are less common. Tell the team at once if you get a rash that spreads, swelling of the face or difficulty in breathing, which can be signs of a rare allergic reaction.
About this guide
This guide is by the Pai Hospital Team. Pai Hospital is at Vaddem, Vasco-da-Gama, Goa, with its own operating theatre and IVF laboratory. Consultations are held in Panjim, Margao, Mapusa and Vasco; the scans, the egg collection and the embryo transfer are done at the hospital at Vaddem, Vasco-da-Gama. The fees for IVF and the other fertility treatments are on our IVF cost in Goa page.
This article is for education only and is not personal medical advice; please speak to your own doctor about your situation.
Your questions
What happens if I take cetrorelix late?
Call the hospital straight away. A dose taken well outside the 24-hour window may let an early LH surge slip through, so the doctor may want an extra scan or blood test and will tell you what to do next.
Can I give the cetrorelix injection myself?
Yes. Most women, or their husbands, learn to give it at home after the nurse shows them how. The ready-filled syringe needs no mixing at all.
Is cetrorelix used in IUI?
Not usually. In IUI the egg is meant to be released into the tube, so an injection that holds back ovulation is rarely needed. It belongs mainly to IVF, where the eggs are collected directly from the ovaries.
How many cetrorelix injections are needed in IVF?
Usually a few, often three to five, one each day from the time the lead follicle reaches about 14 mm until the trigger. The exact number depends on how your follicles grow.
How long does cetrorelix act in the body?
Its effect wears off within about a day after the last dose. That is why it has to be taken every day while it is needed, and why it can simply be stopped at the time of the trigger.
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This page is for general education and is not personal medical advice. Treatment depends on your own examination and reports, so please speak to a doctor about your situation. We do not carry out or offer sex determination of any kind.