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As we have previously discussed, in a natural cycle, FSH is secreted from the pituitary gland in the brain into the bloodstream and acts on the ovary to cause the development of the egg in the follicle. The follicle secretes estrogen which, in turn, causes the lining of the uterus (endometrium) to thicken in the first two weeks of the cycle. When the follicle secretes enough estrogen, the pituitary interprets this as a signal that the follicle and the egg are mature and the egg will fertilize. The pituitary then secretes a second hormone, LH, in a surge into the bloodstream and causes ovulation in 24 to 36 hours.
When we do IVF, GIFT or Fertility Preservation, our goal is to stimulate many follicles containing eggs and the estrogen (estradiol) level may become quite high and signal the LH surge prematurely. This would cause premature ovulation before we are ready to do the egg retrieval.
To prevent this, we use a class of medication called gonadotropin antagonists to prevent this premature LH surge. The two available medications are Antagon or Cetrotide which are virtually identical but made by two different pharmaceutical companies. One of these medications, which is also given by injection just like Follistim or Gonal-F, will be started on the 5th or 6th day of stimulation. There are no side effects to these medications and they are cleared out of the body in about 24 to 36 hours. Therefore, there would be no adverse effects should you become pregnant.
Go to: Micro-Manipulation Procedures
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