Trigger injection (human chorionic gonadotrophin)
Pregnyl
Also known as Human chorionic gonadotropin (hCG)
Pregnyl contains human chorionic gonadotrophin (hCG), derived from urine, given by injection to finish the maturing process of the eggs before retrieval.
Why it may be used
Like other hCG-based trigger medicines, it is used to complete egg maturation and to fix the timing of ovulation, so that egg retrieval can be planned precisely.
Where it fits in a cycle
It is given as a single injection near the end of the stimulation phase, at a time set by your clinic based on your scan and blood results. Egg retrieval is scheduled around this exact timing.
Side effects listed in the patient leaflet
- Injection site pain, redness or bruising
- Headache
- Abdominal discomfort or bloating
- Nausea
- Fatigue
- Mood changes
- Ovarian enlargement or tenderness after the trigger
When to ring the clinic
- •Rapid or severe abdominal swelling after the injection
- •Severe abdominal or pelvic pain
- •Breathlessness
- •Passing much less urine than usual
- •Sudden weight gain, which can indicate OHSS
Questions people ask
- Why does the timing matter so much for this injection?
- Egg retrieval is planned around a set number of hours after this injection, so confirm the exact time with your clinic and follow it precisely.
- Does Pregnyl need mixing before use?
- Some presentations require reconstituting with a diluent before injecting. Follow the leaflet in the box and your clinic nurse's instructions.
- Will it affect a pregnancy test result?
- It contains hCG and can cause a false positive on a home test for some time afterwards, so ask your clinic when testing is appropriate.
- What if the injection does not go as planned?
- Contact your clinic straight away, since this affects the timing of your retrieval.
Safety
- This is general information only and is not a substitute for advice from your clinical team.
- Timing must be confirmed with your own clinic, since it is closely tied to egg retrieval scheduling.
- The patient information leaflet in the box is the authoritative source for this medicine.
- Tell your clinic about other medicines, allergies and medical conditions before use.
Read next
Sources
- Patient information leaflets and product characteristics, electronic medicines compendium (emc). Link checked 17 September 2026.
- IVF: what is IVF and how does it work?, HFEA (UK fertility regulator). Link checked 17 September 2026.
Written by patients, not clinicians. This page has not yet been reviewed by a named fertility professional, so it explains published guidance and points you to the original source instead of giving medical advice. It is not medical advice. Decisions about your treatment belong with your own clinic. Read our editorial policy and corrections policy.