Trigger shot performs a critical function in IVF treatment. The aim of an IVF trigger shot is to send the eggs into a state of reproductive cell division known as meiosis. Additionally, eggs start maturing during the 36-hour length before ovulation or oocyte retrieval. The timing and efficiency of this method determine the quality of eggs to be retrieved.  It helps in embryo advent and the final results of the cycle. When it involves ovulation induction for IVF treatment, we should select and implement the trigger shot with utmost care. It is one of the most important choices a doctor must make because it significantly affects the success rate of the IVF cycle.

What is a trigger shot for IVF?

               The trigger injection or ‘trigger shot’ as it’s also known, is a hormone injection. It is utilized in fertility treatment and usually consists of a hormone known as human chorionic gonadotropin, or u -HCG. It is HCG which triggers a follicle to mature and release the egg. In maximum cases the trigger shot needs to be taken 36 hours earlier than egg collection, or an afternoon and a ½ day prior. The trigger shot timing is in synchrony with the improvement of follicles.It has to be completed when a good range of follicles have grown to their greatest size. Under or overdeveloped eggs have a decreased risk of conception success.

Alternative shots to U- HCG 

  1. GnRH analog : Gonadotropin-releasing hormone agonist (GnRH-a) trigger has been used for the induction of final follicular maturation. It aims at ovulation with reduction of the OHSS risk. GnRH-a trigger stimulates FSH secretion in addition to LH surge. The advantage of this method is more maturity of the nucleus and the resumption of meiosis. Eventually it increases the number of Metaphase II oocytes. It is useful in patients under antagonist protocol only. Those under long agonist protocol won’t respond to it.
  2. Recombinant HCG – Recombinant fertility drugs are made in a laboratory using DNA technology. They are much similar to hormones made by the body in molecular composition. In the case of r-hCG, the lab-made hormone is similar to the body’s natural luteinizing hormone (LH). It is not recommended in people with primary ovarian insufficiency or those with very poor ovarian reserves. The fertility drugs in general may not be effective for these people. Since recombinant LH has a shorter half-life compared with hCG, its use also helps luteal support while potentially reducing OHSS risk.

Will the trigger injection be painful?

There are various methods of administering the trigger injection. It can both be given into the muscle (intramuscular) or below the skin (subcutaneous), that’s the maximum common route. An intramuscular injection will be similar to getting a vaccine shot at your GP and might cause more bruising than while injecting below the skin. Women on occasion report redness of the area of subcutaneous injections. It can make the site turn out to be red, inflamed and itchy for a day. However, these side effects post injection are usually minimal.

Potential side effects of a trigger shot

                   Most women now no longer experience any side effects following the trigger injection.  Possibly some transient local irritation on the injection site is seen. At this level of treatment, it is not unusual to have been already experiencing some stomach pain or slight bloating. These are because of the blended impact of the hormones and the growth in the size of the follicles in ovaries. Following the trigger injection, these symptoms may be exaggerated. As this isn’t supposed to be an exhaustive list of side effects, you should not hesitate to seek advice for any new symptoms.

How does the trigger shot work for IVF?

Gonadotropin Stimulation

The trigger shot is in fact human chorionic gonadotropin (HCG), a hormone that stimulates the follicles to rupture and release an egg. In an ovarian stimulation cycle; gonadotropin hormones including FSH and LH stimulate the ovaries for egg development. The trigger shot should be administered about 36 hours earlier than IVF egg retrieval because the timing is essential for the fulfillment of the whole IVF process. HCG injection makes the egg mature and detach from the cumulus oophorus. This makes the mature egg to float in the fluid which can be easily picked up during aspiration of follicles in IVF.

Maturation of Egg Cell

The aim of the trigger shot in IVF treatment is to send eggs into a reproductive division called meiosis. During meiosis; the goal is to prepare the egg cell for division. It lowers the number of chromosomes in the eggs from forty six to twenty-three prior to egg retrieval or ovulation. Trigger shots expels some of the chromosomes from the egg’s nucleus into a membranous envelope. This so-referred to as the first polar body. This organelle lies below the envelope of the egg in an area called perivitelline space. Embryologists use this polar body to identify a mature egg. Here it appears as though the cells surrounding the egg are eliminated through microsurgery, but they erode on their own under effect of HCG. 

Microscopic visualization

Microscopic visualization of the polar body confirms that the eggs are mature, that means it has gone through meiosis. However, it presents no assurance that there are only 23 chromosomes remaining in the egg’s nucleus. If precisely 23 chromosomes aren’t present then the fertilized egg will create an aneuploid embryo. An Aneuploid embryo is one which has an abnormal quantity of chromosomes (extra or much less than forty six) and is incapable of making a healthy baby. Hence, the dosage, method, and management of the trigger shot have an effect on the ability to yield mature quality eggs. The stated trigger shot elements additionally constitute a rate-limiting step in ovulation induction specifically for the IVF treatment cycle.

Dosage of the trigger

Many clinicians face the risks of OHSS in women with more follicles. They deliberately pick to reduce the dosage of HCG administered as trigger shot. Doing so considerably reduces the chance of growing critical OHSS. However, a low dose of HCG (5,000 units) is in all likelihood to be insufficient to optimize the performance of meiosis, mainly when there are numerous follicles.

HCG trigger shot mistakes

In few cases when the trigger injection is given in a lower dose it does not yield eggs. This condition is called Empty follicle syndrome. Empty follicles are more common in elderly patients with poor ovarian reserve, in a flare protocol or inadequate dosage. At times, a break in the cold chain makes the drug ineffective. If there are errors in mixing or spill during administration desired effects are not achieved. Hence, EFS phenomenon can be due to premature ovulation, low ovarian reserve, or hCG-related errors. 

Timing of the trigger shot during IVF

             This needs to coincide with the maximum of the ovarian follicles being more than 15 mm in diameter. It may happen so with numerous follicles having reached 18 to 22 mm as well. The follicles develop an average of two mm in a day with optimum stimulation. Follicles larger than 22 mm will typically harbor overdeveloped eggs, which may possibly fail to fertilize. Follicles less than 15 mm contain underdeveloped eggs which may be more likely to be incompetent following the trigger.

Does trigger shot release all mature eggs?

The protocol decided on for ovarian stimulation is one of the most critical elements of IVF treatment due to the fact that most beneficial egg maturation depends on earlier egg development. Unless the follicles and eggs grow optimally, no trigger shot is probably able to yield accurate quality eggs.

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