These drugs are used to avoid the premature luteinization of follicles and control the ovulation date so that it does not occur too early.
Its administration may cause the following effects:
- GnRH antagonists binds to the receptor, therefore GnRH cannot bind (compet
itive blockage). Receptors are placed in the surface of the pituitary gonadotrope cells.
- It blocks the synthesis of gonadotropins (FSH and LH) by the hypophysis, since it blocks GnRH receptors.
- They have an immediate onset of action.
- It prevents the flare-up effect of GnRH agonists to occur.
Prescription of GnRH antagonists is indicated in the following cases:
- Women over age 37.
- Poor-responders: women who presented a low response to ovarian stimulation (i.e. the number of ripe follicles) in previous assisted reproduction cycles and, therefore, the number of eggs obtained after follicular puncture was too low.
- Women at increased risk of ovarian hyperstimulation syndrome (OHSS).
- Where the immediate cancellation of endogenous gonadotropins (FSH and LH) production is required.
The advantages of this medicine in assisted reproduction cycles are mentioned hereafter:
- It causes the immediate cancellation of LH serum levels, preventing thus premature ovulation.
- It implies a shorter duration of the ovulation induction treatment.
- It is usually well tolerated by women. It has few side effects, since the stimulation process is not very aggressive.
- A lower dose of FSH is administered.
- It decreases the frequency of ovarian hyperstimulation syndrome (OHSS).
- Woman’s recovery of the pituitary function occurs faster, which means it will not affect new stimulation treatments in future cycles.
- It does not cause follicle cysts, since it prevents the flare-up effect which GnRH agonists would cause.
The use of GnRH antagonists involves few disadvantages, since it is well tolerated by most women with virtually no contraindications mainly because the stimulation process is not very aggressive.
The only problem is that its pregnancy rate is slightly lower (between 3% up to 5% less) than that obtained by means of ovarian stimulation protocols, where GnRH analogues are used due to the effect of the antagonists on the endometrium, the Fallopian tubes, the follicle, and the oocyte.
Medicines containing GnRH antagonists which are typically prescribed in assisted reproductive treatments are Cetrotide and Orgalutran.