Ideal egg development sets the scene for optimal egg maturation that occurs 36-42h prior to ovulation or egg retrieval. Without prior optimal egg development (ovogenesis), egg maturation will be dysfunctional and most eggs will be rendered “incompetent” and unable upon fertilization to propagate viable embryos. In IVF, optimal ovogenesis requires the selection and implementation of an individualized approach to controlled ovaria stimulation (COS). Thereupon, at the ideal time, maturational division of the egg’s chromosomes (i.e. meiosis) is “triggered” through the administration of hCG or an agonist such as Lupron, which induces an LH surge. The dosage and timing of the “trigger shot” profoundly affects the efficiency of meiosis, the potential to yield “competent” (euploid) mature (M2) eggs, and as such represents a rate-limiting step in the IVF process.
Triggering meiosis with Urine-derived hCG (Pregnyl/Profasi/Novarel) versus recombinant hCG (Ovidrel): Until quite recently, the standard method used to “trigger” egg maturation was through the administration of 10,000 units of hCGu. Subsequently, a DNA recombinant form of hCGr (Ovidrel) was introduced and marketed in 250 mcg doses. But clinical experience strongly suggests that 250 mcg of Ovidrel is most likely not equivalent in biological potency to 10,000 units of hCG. It probably only has 50%-70% of the potency of a 10,000U dose of hCGu and as such might not be sufficient to fully promote meiosis, especially in cases where the woman has numerous follicles. For this reason, I firmly believe that when hCGr is selected as the “trigger shot” the dosage should best be doubled to 500 mcg at which dosage it will probably have an equivalent effect on promoting meiosis as would 10,000 units of hCGu. Having said this, it is my personal opinion that it is unnecessary to supplant hCGu with hCGr since the latter is considerably more expensive and is probably no more biopotent than the latter.
Some clinicians, when faced with a risk of OHSS developing will deliberately elect to reduce the dosage of hCG administered as a trigger in the hope that by doing so the risk of critical OHSS developing will be lowered. It is my opinion, that such an approach is not optimal because a low dose of hCG (e.g., 5000 units, hCGu or 25omcg hCGr) is likely inadequate to optimize the efficiency of meiosis particularly when it comes to cases such as this where there are numerous follicles.
It has been suggested that the preferential use of an “agonist (Lupron) trigger” in women at risk of developing severe ovarian hyperstimulation syndrome could potentially reduce the risk of the condition becoming critical and thereby placing the woman at risk of developing life-endangering complications. It is with this in mind that many RE’s prefer to trigger meiosis by way of an “agonist (Lupron) trigger rather than through the use of hCG. The agonist promptly causes the woman’s pituitary gland to expunge a large amount of LH over a short period of time and it is this LH “surge” that triggers meiosis. The problem with using this approach, in my opinion, is that it is hard to predict how much LH will be released in by the pituitary gland. For this reason, I personally prefer to use hCGu for the trigger, even in cases of ovarian hyper stimulation with one important proviso – she underwent “prolonged coasting” in order to reduce the risk of critical OHSS, prior to the 10,000 unit hCGu “ trigger”.
The timing of the “trigger shot” to initiate meiosis: This should coincide with the majority of ovarian follicles being >15 mm in mean diameter with several follicles having reached 18-22 mm. Follicles of larger than 22 mm will usually harbor overdeveloped eggs which in turn will usually fail to produce good quality eggs. Conversely, follicles less than 15 mm will usually harbor underdeveloped eggs that are more likely to be aneuploid and incompetent following the “trigger”.