Trigger shot injections: your questions answered

When going through IVF, the trigger shot is an important stage in the process, marking the end of ovarian stimulation medication and helping your ovaries with the final maturation of your eggs before they are retrieved during a short egg collection procedure.

Your fertility consultant will tell you when and how to administer your trigger shot but even so, you may have extra questions about this part of your IVF journey. This guide answers common IVF trigger shot questions to help you feel fully informed and put your mind at ease.

What is a trigger shot?

The trigger injection or ‘trigger shot’ as it is also known, is a hormonal injection used in fertility therapy. Brand names in the UK include Choragon, Ovitrelle, and Pregnyl, among others. A trigger shot usually contains a hormone called human chorionic gonadotropin, or HCG. It is hCG which triggers an ovary to mature and release an egg.

Why do I need a trigger shot?

Women undergoing IVF treatment do a trigger shot so that eggs are matured for collection. Once you have the injection, your ovaries are sent into a cycle of development which allows for egg collection at a specific time which will be outlined by your fertility team.

What does a trigger injection do in IVF?

The trigger injection contains a hormone called human chorionic gonadotropin (hCG). Many people call hCG the ‘pregnancy hormone’ as it is produced by the placenta during pregnancy and is what is detected with a pregnancy test.

When used as an IVF trigger shot, hCG actually behaves more like the luteinising hormone (LH) that is produced in the pituitary gland. LH is secreted by the pituitary gland just before ovulation and is crucial in helping the developing egg to mature and prepare to burst out from the ovary. The trigger shot sets off the same process, albeit artificially.

The trigger shot also initiates meiosis. During meiosis, your eggs shed half of their chromosomes, going from 46 to 23. This is necessary so that the 23 chromosomes in each sperm cell can combine with each egg for fertilisation.

Do follicles grow after the trigger shot during IVF?

Yes, follicles can continue to grow between when you take your trigger shot and the time of your egg retrieval. The trigger shot is carefully timed based on the size of your follicles. If several follicles are at the optimum size (usually between 15mm and 22mm), the trigger shot is scheduled to allow final maturation of these follicles’ eggs. However, if you have some follicles that are slightly smaller, the trigger shot can enable these to ‘catch up’ and reach optimal size too.

When should I take the trigger shot?

You will be given careful guidance on this topic by your Apricity advisor. It is important to follow the timing instructions exactly as delays of just a few hours can cause issues with your treatment cycle. Essentially, in most cases the trigger shot needs to be taken 36 hours before egg collection, or a day and a half prior. So if you have a midday appointment for egg collection on Tuesday, you would take the trigger shot at midnight on the Sunday prior. There are some variations to this time window and your advisor will inform you if your case is one of those.

 The trigger shot timing is in line with the development of your follicles, which your clinical team will have been tracking. The trigger shot tends to be done when a good number of follicles have grown to their optimal size. Under or overdeveloped eggs have a lower chance of conception success.

Do I inject trigger shots myself?

Generally yes, especially as the 36 hour window from injection to collection often means the shot is usually taken in the evening and sometimes late in the evening. We ensure that an Apricity advisor is available at the time of the injection in case you have any last minute questions.

I have missed my trigger shot. What do I do?

If you are late taking your trigger shot, it is imperative you let your Apricity advisor or clinic know as soon as possible, as there may be things that they can do to try and salvage the situation. It is not possible to retrieve an egg after the ovary has released it, so it’s important to try and resolve this as soon as possible. In certain circumstances, it may be feasible to adjust your egg collection time.

How painful is the trigger shot for IVF?

There are two ways of administering the trigger injection. It can either be given into the muscle (intramuscular) or under the skin (subcutaneous), which is the most common route. An intramuscular injection will feel the same as getting a vaccine shot at your GP and can cause more bruising than when injecting under the skin. 

How painful the trigger shot is does vary from person to person, but most individuals don’t experience discomfort but may feel a slight sting or pinch, much like when receiving any other injection. Women occasionally report that subcutaneous injections cause the site to become red, inflamed and itchy for a day or two. Either way, the side effects immediately post injection are usually minimal.

How long after the trigger shot is IVF?

Usually when someone refers to IVF, it is in relation to the entire process starting from the initial blood tests and baseline scan through to egg transfer. The trigger shot typically occurs 8-12 days into an IVF cycle.

However, IVF can also refer to the specific in-vitro fertilisation procedure where an embryologist combines retrieved eggs with sperm outside of the body, in a laboratory setting, to create embryos. This procedure is carried out directly after egg collection, which is normally scheduled for 36 hours after the trigger shot is administered. After the eggs and sperm have combined to form embryos, they will be carefully monitored for 3-6 days before one or more is transferred back into the womb and any remaining embryos are frozen.

Potential trigger shot side effects

Most women do not experience any side effects following the trigger injection, apart from perhaps some local irritation at the injection site, which is usually transient. At this stage of your treatment, it is not uncommon to have been already experiencing some abdominal discomfort or mild bloating due to the combined effect of the treatment hormones and the increase in the size of the ovaries. Following the trigger injection, these symptoms can sometimes increase. As this is not intended to be an exhaustive list of side effects, do not hesitate to seek advice if you are concerned about any new symptoms.

Make sure to monitor any abdominal discomfort or bloating as this can sometimes be associated with Ovarian Hyperstimulation Syndrome (OHSS), which can become serious if left untreated. Other symptoms of OHSS include blood clots, difficulty breathing and reduce urination. If you have any concerns about your trigger shot, you can contact your Apricity advisor.

At Apricity, our patients have instant access to their medical teams 7 days a week so that they always have the support they need. So, if they have a question about their trigger shot or anything else, they can chat to an advisor and browse our fertility guidance and resource hub directly from their phones. If you’re interested in finding out more about our inclusive at-home care or our IVF treatment packages, you can book a free consultation with an Apricity advisor today.