Sunday, 8 June 2014
Alternative trigger shot
Trigger shot is essentially to facilitate retrieval of eggs which up until the final maturation are attached with a stalk to the wall of the follicle. After trigger injection, the final maturation starts and the eggs complete their maturation division. Also the egg is released into the follicle fluid. Unless this happens, all the efforts of stimulation would be futile as lesser number or no eggs will be obtained at egg collection procedure. The traditional shot consists of hCG (or pregnancy hormone). The way it works has been explained in my previous post: IVF trigger shot.
What is the need for an alternative? It is the very real and very serious risk of OHSS (also discussed in a previous post: Is too much stimulation good?). In order to negate the risk of OHSS, an alternative trigger shot can be used. This is in the form of GnRH agonist. I have explained how agonists and antagonists work in my post: How is ovulation prevented in IVF?
The alternative trigger shot can only be used in antagonist cycles, in those women who are at risk of OHSS or those who are going through a egg donation cycle. Agonists 'trigger' a response from the pituitary in the form of release of a large amount of LH. This causes the final maturation in the follicles. As the life of LH is much shorter than hCG molecules, the risk of OHSS is very limited and short lasting with this protocol.
Women who have agonist as a trigger, should have a modified luteal phase support as otherwise the pregnancy rates are lower and miscarriage rates are higher. In my opinion, in the strife to eliminate OHSS, patients should be adequately counselled with respect to freezing of all embryos. My reason is that even if pregnancy occurs in these women, they are still at a risk of secondary OHSS which occurs from the pregnancy hormone released from the new pregnancy that has implanted. These symptoms will take much longer to abate in the background of an ongoing pregnancy!