GnRH Analogues

GnRH analogues are used in the main Assisted Reproductive Technologies (ART), such as AI, IVF, and ICSI. These drugs are used to prevent early follicular luteinisation and to regulate the date of ovulation so that it does not occur prematurely.

Effects

The main effects of GnRH analogues are:

  • Quick release of gonadotropins: the binding between the GnRH analogue and its receptor provokes an immediate release of the FSH (follicle-stimulant hormone) and LH (luteal hormone) hormones.
  • Temporary blockage of gonadotrophins release: this occurs in the hypophysis because the stock of FSH and LH is empty, preventing the hypophysis to communicate with the ovary, a process that would have an effect on ovulation. It takes place 5 to 10 days after its first administration.

These two effects are enough the synchronise the follicles recruited by the ovary, favoring an homogeneous follicular growth and lowering the variability of the ovarian response.

Indications

The prescription of GnRH analogues is especially indicated in the following situations:

  • In women who have had low quality oocytes during past cycles. Early LH peaks are prevented. Early LH peaks provoke early follicle luteinisation, and that leads to poor oocyte quality.
  • Women with polycystic ovary syndrome (PCOS) and elevated basal blood LH levels.
  • Women with polycystic ovary syndrome (PCOS) and a high blood androgens levels.

Advantages

The main advantages of the administration of GnRH for ovulation stimulation are:

  • Lower cancellation rates.
  • LH levels, resposible for ovulation, will decrease.
  • Follicle growth is quite homogeneous, lowering the variability of the response.
  • High amount of oocytes obtained from the ovarian puncture, the number of grown eggs to be fertilisated increases as well as the number of embryos that can be obtained in every menstrual cycle.
  • A sharp increase occurs in pregnancy rates probably due to the local effect that GnRH analogues produce on the ovaries and the endometrium.

Disadvantages

Disadvtanges of using GnRH for ovarian stimulation in the assisted reproduction cycles are:

  • The risk of having ovarian hyperstimulation syndrome increases due to the flare-up effect.
  • Insufficiency in the luteal body is more likely to happen; therefore, in order to have the endometrium ready to receive the embryos, it is necessary to administer another hormone called progesterone so that the endometrium thickens.
  • It may lead to the formation of ovarian cysts.
  • Greater chances of having a multiple pregnancy with all the risks associated with this kind of pregnancy.

GnRH drugs commonly prescribed in assisted reproduction treatments are: Decapeptyl, Synarel, and Procrin.

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