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Thursday, 29 May 2014

IVF trigger shot

IVF trigger shot is the last injection that is given approximately 36 hours before the egg collection. This is one of the most crucial steps of IVF and if done incorrectly or missed will prevent retrieval of eggs.

"Why trigger?" and "Trigger what?" are the most natural questions that would come to mind. The eggs that are developing in the growing follicles during ovarian stimulation are not fit to form an embryo. They have not yet completed their maturation division that leads to halving of the number of chromosomes. This has been discussed already in my earliest posts. In addition, the egg encased in the clump of cumulus cells (called COC or cumulus oocyte complex) is still attached by a stalk to the wall of the follicle. Till such time that this stalk is intact, aspiration of follicle fluid will not yield the egg that is present in the follicle.

In the natural cycle, these final events and the ovulation are triggered by the release of a large amount of LH hormone (called LH surge) from pituitary gland. In IVF cycles the natural release of hormones from pituitary gland are restricted due to the IVF medicines (as explained in my previous post on agonists and antagonists). Hence there is a need to artificially facilitate these important steps.

The trigger injections are in the form of Human Chorionic Gonadotrophin (hCG) which is the same as pregnancy hormone. This hormone is very similar to LH in structure and so can carry out the functions of an LH surge. Based of the source, hCG comes is of two types: urinary and recombinant. Both are equally effective. Recombinant hCG however is a little more expensive than urinary for obvious reasons.

Alternative trigger injection in the next post....

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