An important determinant to improve egg quality goes through meiosis, also known as maturation division. During the 36-hour period that precedes the ovulation, the efficiency for IVF will determine the retrieval process and the outcome of the reproduction. When it comes to ovulation induction, along with selecting a suitable protocol for ovarian stimulation; choosing and implementing the trigger-shot is one of the most important decisions a clinician must make. This trigger shot facilitates meiosis.
The Timing of The Trigger Shot to Initiate Meiosis
This must coincide with most of the ovarian follicles. Greater than 15 mm in diameter and with several follicles having reached 18 t0 22 mm. Follicles larger than 22 mm will be usually harbor over developed eggs. Which in turn are most likely to fail to produce good quality eggs. Follicles less than 15 mm will also harbor underdeveloped eggs that are most likely to be incompetent following the trigger.
The protocol finalized for ovarian stimulation is one of the most important aspects of IVF. The reason is optimal egg maturation is predicted upon prior egg development. Optimal development of eggs are necessary otherwise no trigger-shot by itself will be capable of yielding good quality eggs.
Ovarian Stimulation Cycle to Improve Egg Quality for IVF.
Here’s how it works:
Egg development takes place during the gonadotropin stimulation stage. About 36 hours prior to egg retrieval, a trigger-shot must be administered. This trigger shot contains one of three medications:
- Urinary derived hCG (hCGu) such as Noravel, Pregnyl, and Profasi.
- Recombinant hCG (hCGr) such as Ovidrel.
- An agonist such as Lupron which provokes a surge in the release of pituitary gland upon injection.
The purpose of the trigger shot is to send eggs into a reproductive division or meiosis. The objective is to decrease the number of chromosomes in the eggs from 46 to 23 prior to ovulation. It expels almost half of the chromosomes from the egg’s nucleus in a membranous envelopment. This so-called first polar body comes to lie under the envelopment of egg in a region known as perivitelline space. This is where one can observe it microscopically once microsurgery removes the cells surrounding the egg. They can also erode on their own.
Confirmation of Egg Maturation
Microscopic visualization of the polar body confirms that the egg is mature (has gone through meiosis). It provides no assurance that there are only 23 chromosomes remaining in the egg’s nucleus. Now, if exactly 23 chromosomes are not remaining in the nucleus of the egg after fertilization, it will be unable to propagate a euploid embryo (one with 46 chromosomes). An embryo with an irregular number of chromosomes (more or less than 46) is known as aneuploid or “incompetent”. This means it is incapable of propagating a healthy baby.
Meiosis that takes place after the administration of trigger shot, is indispensable to the normal reproductive process. Hence, the dosage, method, and timing when the trigger shot is administered affect the potential to yield mature eggs. It also represents a rate-limiting step in ovulation induction specifically for IVF procedures.
Urinary Versus Recombinant hCG1
Several years ago, the standard method that was in use to initiate the trigger shot was the administration of 10000 units of hCGu. More recently, a recombinant form of hCG (Ovidrel) was introduced in 250 mcg doses. But experience suggests that that 250 mcg is not equivalent in biological potency to 10000 units of hCG. The potency is probably only 50% to 70% as compared to 10000 doses of hCGu. This might not be enough to fully promote meiosis, especially in cases where a woman has numerous follicles. For this reason, it’s firmly believed that the dosage needs to be double (500 mcg) when selecting hCGr as the “trigger shot”. At this dosage, it will have the same effect as 10000 units of hCGu. Having said this, it is unnecessary to supplant hCGu with hCGr since the latter is more expensive and is no more potent than the former.
Dosage of hCG
Many clinicians, when faced with the risks of OHSS developing, deliberately elect to reduce the dosage of hCG administer as a trigger shot. In doing so, the hope is that the risk of developing critical OHSS will be reduced. But such an approach is not optimal because a low dose of hCG is likely to decrease the efficiency of meiosis. This can be 5000 units of hCGu or 250 mcg hCGr, particularly when it comes to cases when there are numerous follicles.
Use of hCG Versus an Agonist as The Trigger Shot
Experts has suggested that the use of an agonist, such as Lupron as a trigger shot, could reduce the risk of severe ovarian hyperstimulation. This also reduces the risk of the situation becoming critical and the development of life-endangering complications. It’s for this reason that many prefer to trigger meiosis this way rather than the use of hCG. Lupron causes the women’s pituitary gland to expunge a large amount of LH over such a time and it’s this surge that triggers meiosis.
Although there’s a problem with this approach. It’s hard to predict how much LH will the pituitary gland release for a patient receiving Lupron as trigger shot. Especially if the patient undergoes down regulation using an agonist (Lupron) or where the antagonist was used to block pituitary LH release. For this reason, it is preferable to use hCGu for the trigger, even with ovarian hyperstimulation, with one important proviso that she underwent ‘prolonged coasting’ in order to reduce the risk of critical OHSS prior to the 10000-unit hCGu trigger.
Side effects of the trigger shot
There are some side effects which you might experience while using and after having used the trigger shot. Most common include bloating and stomach/pelvic irritation. You may also experience pain or tenderness around the injection site.
Mild cases may give you abdominal discomfort, bloating, and gastrointestinal issues, like nausea, vomiting, or diarrhea.
Although rare, OHSS also poses a risk. With OHSS, your ovaries swell and fill with fluid. Severe OHSS is even rarer but can call for a medical emergency. The symptoms include fast weight gain (over 2 pounds a day) and abdominal bloating, as well as extreme discomfort in your abdomen or extreme nausea/vomiting.
Other possible signs you may face:
- Blood clotting
- Difficulty in breathing
- Low urine output
You can visit our website to find useful information about Egg Donation, Egg Freezing & IVF. You can also call us at 858-436—7186 to schedule a consultation with RSMC fertility clinic, California.
