Endocrine Abstracts

Achieving pregnancy through in vitro fertilization requires a minimum number of oocytes recovered during egg retrieval. These oocytes come from ovarian hyperstimulation that allows the entire oocyte cohort to mature. In physiology in a natural cycle, a dozen follicles are recruited at the beginning of the menstrual cycle under the action of the elevation of the FSH (the « FSH window »). Then, follicles secrete estradiol through aromatase under the action of FSH. By negative feedback, FSH levels decrease (the FSH window closes) and only the follicle most independent of FSH will continue to grow until ovulation: the dominant follicle. The other follicles of the cohort attenuate allowing mono-ovulation. On the contrary, it is very important in the process of in vitro fertilization to have a multifollicular development, in order to increase the chances of pregnancy. Indeed, there are still many stages before pregnancy: puncture and selection of oocytes, obtaining fertilization and then a quality embryo to be transferred. The goal of the treatment is therefore to continue the administration of FSH to avoid the closing of the window and thus allow the maturation of all the follicles of the cohort. The other very important aspect of stimulation treatment during IVF is to control the exact time of ovulation. GnRH agonists or antagonists are used but the use of simple progestins is also possible! Finally, the triggering of ovulation is achieved through the administration of either hCG (with an LH like action) or a GnRH agonist in cycles slowed down by GnRH antagonists. Completely artificial cycles are also possible to transfer devitrified embryos.