What is a trigger shot?

9 fertility expert(s) answered this question

Answer from: Halyna Strelko, MD

Gynaecologist, Co-founder& Leading Reproduction Specialist
IVMED Fertility Center

A trigger shot is the most important injection during the cycle and the most responsible injection because without a trigger shot we will not receive any egg. It is important to know the principle of this injection. First, this injection should be done 35 – 36 hours before the egg collection. If, for example, a patient forgets, loses or changes time or doesn’t do it at all – it is mandatory to say to the doctor who is doing the stimulation about that. If the doctor will know before the egg collection, there is a possibility to change something and to finally receive eggs – maybe not the time which was planned but at least we will receive eggs. If a patient will not do this injection correctly or not in time, we will not have eggs. So, 35-36 hours, is important to say if something was done incorrectly.

We have two types of injection: one type, old one. If we can say HCG Human Chorionic Gonadotropin, it means that it is the substance which is produced during pregnancy but this substance activates LH receptors. LH receptors should be activated for final egg maturation so, this substance acts like LH – it is not LH but acts like LH. The HCG, this molecule has a very long period of half-life, which means that one injection will be detected in blood circulation during 10 -11 probably 12 days. This molecule not only activates the LH receptor but also has the possibility to have FSH like effect. It means that 10 days after injection we like to continue the stimulation. Also it activate some kind of receptors which increase the vessels permeability and liquid plasma from vessels come to abdomen cavity to pericard, to lungs whatever and ovarian hyperstimulation syndrome – big ovary, very high estradiol, increased coagulation and not enough liquid inside of vessels and liquid in abdomen and in the cavity – this is ovarian hyperstimulation syndrome. So, this molecule may produce good quality eggs but may give a lot of problems.

Another kind of injection is agonists of GNRH. We are using them to increase LH, we do the injection and LH rises so it is more natural. It does not have this effect of 10 days in blood circulation, big ovaries, etc. So, as we have quite short peaks of LH after 48-72 hours ovaries decrease their activity after egg collection and normally we never have hyperstimulation with this kind of injection. So it is very safe but with this kind of injection we usually will never have pregnancy in the fresh cycle. So, with this injection necessary to take eggs, fertilize, produce embryos and freeze, have a rest and come to see a doctor in a couple of months and do the transfer.

Answer from: Valentina Denisova, MD PhD Obstetrician Gynaecologist

Gynaecologist, Fertility Specialist
Next Generation Clinic

The trigger shot is the main injection in our stimulation; it is needed to retrieve mature oocytes. So, this shot is usually prescribed in the late evenings and the ovarian puncture is performed 36 hours after this shot, as the time is needed for oocyte maturation.

Answer from: Guillermo Quea Campos

Gynaecologist, Specialist in Reproductive Medicine
Pronatal Fertility Clinics

We use a trigger shot but in some cases not always.  We have policies about vitrifying embryos to avoid the ovarian hyperstimulation syndrome in any cases or we are going to freeze them all to improve our outcomes in the treatments. Right now to use the double trigger it’s a very good procedure nevertheless we have another procedure to improve our outcomes. That’s the reason why normally we don’t use this trigger

Answer from: Christos Kleanthis, MD MSc PhD

Gynaecologist, Obstetrician and Reproductive Gynecologist

Trigger injection contains the medication that will lead to the final maturation of the eggs before we collect them on the collection day. There are mainly two categories of trigger injections: the first category, hormones that we naturally have that lead to maturation and the second one, causes the rise of the natural hormones that we have in our bodies to mature the eggs. By double trigger, we mean that we use both this medication to induce maturation, final maturation to oocytes and the main difference is the lasting effect. The one that causes our natural hormones to rise, has a shorter effect compared to the one that mimics the effect of our natural hormones.

Answer from: Christos Kleanthis, MD MSc PhD

Gynaecologist, Obstetrician and Reproductive Gynecologist

A trigger shot is the medication that leads to the final maturation of the oocyte during in vitro fertilization treatment. There are various medications that can cause this maturation with a longer or shorter effect on the maturation process.

Answer from: Ahmed Elgheriany, MRCOG, MD, MSc

Gynaecologist, Fertility Specialist
GENNET City Fertility

Triggers shot in endometriosis. We are using two kinds of trigger shots: one of them called the agonist trigger shot is just like the natural hormones coming from your body and the other kind it’s called the human chorionic gonadotropin (hcg). It’s the same as the pregnancy hormone that will rise later on. This one is an exaggerated response from your body to all the symptoms of ovarian hyperstimulation if you will have it after IVF. The first trigger is just like agonist hormones that will just increase natural LH from your brain or maestro gland which are very stimulating and will not have side effects (it’s very safe, very safe medications). That could be used if we’re suspecting to have a polycystic ovary which is not uncommon to be combined with endometriosis.

Answer from: Evangelos Sakkas, MD, MsC

Gynaecologist, Head of Gyncare IVF Clinic
Gyncare IVF Clinic

Trigger shot I don’t know what they really mean by double trigger but there are many things to explain that.
Trigger shot is that you use what one of the three choices we have today or Ovitrell is one of the typical products we have, then Pregni or Gonasi they call it in italy on only case HCG of five or ten thousand (in IVF 10 000 is the second most used triggering) and then what we have after 2012- 2014 under the “Humaidan protocol” we have the Decapeptyl 0.2 so a way in order to avoid OSHH syndrome so Ovitrell, Pregni 10 000 and Decapeptyl 0.2.
In some cases what we say double triggering it’s when we see that we have a very low grade, low percentage of major eggs someone could try to give or the Decapeptyl 0.3 that exists or the Decapeptyl 0.2 and hCG so Gonasi, Pregno 10 000 – that’s a double shot and it achieves it tries to get the maximum of mature eggs possible.

Answer from: Moses Batwala

Gynaecologist, Clinical Director, Consultant Gynaecologist and Fertility Specialist
Sims IVF

Okay, now you got me thinking of my biochemistry and physiology. So this is really in the context of IVF treatment; when you’re doing IVF treatment, what you’re aiming to do, you’re most commonly treating women with injections containing FSH, which is a Follicle Stimulating Hormone. Normally, a woman in her natural menstrual cycle releases one egg, but in the realms of fertility treatment, you’re trying to get her to stimulate, for her to grow anything between 8 to 16 eggs, which you want to collect. So the FSH injections that she takes help make the follicles grow. Each follicle has one egg. Instead of one follicle growing as normal, you’re giving the woman medication to allow anything between 8 to 16, that’s the ideal number you want; 8 to 16 follicles to grow and FSH is very good at making them grow. However, when the follicles reach a certain size, you want to collect them. Normally the body releases a hormone called Luteinizing Hormone [LH] from a small gland in the brain called the Pituitary gland. Women test for this with the urine [LH] sticks. They test for this to know when it’s going to be their fertile window; when they’re about to ovulate, and we try and mimic that by using what we call a trigger shot. It physically allows the egg to be released, that’s the first thing; it physically allows that, but also on a more biological scale, the egg has been kind of dividing to get half the normal number of chromosomes to make it ready to be fertilized by a sperm which also has half the normal number of chromosomes. You and I’m assuming… I’ve tested myself, we have the normal chromosome number which is 46. I have 46 XY chromosomes. That’s what makes me a male. But I got 23 of my chromosomes from my mother and 23 from my father. Now, that happens by the cells in the ovaries dividing in something called Meiosis, to have 23 and 23, and it goes through what we call Two Cell Divisions. The first cell division is covered as the eggs mature, but that last stage for them to move from having the normal number to half the number; it is achieved by a process that is kicked off by that trigger. We call it called Maturation. That’s what really helps the cell move from its normal 46 to the 23 which can then be fertilized, and that’s the importance of that. So physically, it helps release the egg, and also biologically it helps the egg move from 46 chromosomes to 23 chromosomes. Chromosomes are what carry our genes. Genes are what make us what we are; they are the messengers- the genetic messengers that tell us what color our skin is going to be, the color of our eyes, what color our hair is going to be, how tall we’re going to be. All of these are genetic messages that we get from our parents, and this trigger shot helps in the division of the chromosomes to make that egg ready to be fertilized by a sperm.

Answer from: Jessica Subira, M.D. Consultant in Gynecology, Sub-specialist in Reproductive Medicine


The trigger shot is what we give to achieve final maturation of the oocyte. The oocyte is growing inside of the follicle but it’s not mature and it does mature around the time of ovulation. In order to get that maturation, we have to give a second injection of a different hormone and then with that we can achieve the maturation needed to get a mature egg because in the end, we can only work with mature eggs. We cannot really work with immature eggs and we can only freeze mature eggs. It’s very important to get them mature because otherwise they are not viable.

About this question:

What is a trigger shot for fertility?

HCG also known as human chorionic gonadotropin is used in the stimulation process to give a final call for eggs to mature. The simple and more common name for medication that is used in fertility therapy as injectable is a “trigger shot”. Trigger injection can be given in a couple of variations depending on the response and other factors.

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