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In a woman’s regular menstrual cycle, there are three main phases that mark oocyte development. These are:
1- The Follicular phase: This is the phase where the follicles grow and mature
2- Ovulation: This is the exact time a mature egg is released from the follicle
3- The Lutual phase: This phase begins immediately after ovulation, and it is when the body is prepared for a pregnancy by additional hormonal support.
At the time of ovulation, once the mature egg has been released from the follicle, the remaining parts of the follicle then become what is known as the “corpus luteum” cyst.
The corpus luteum functions as a temporary endocrine tissue once pregnancy is achieved. It takes on a very important role which involves production of progesterone, estradiol, and some amount of inhibin A.
Progesterone which is secreted by the corpus luteum is responsible for decidualization of the endometrium. This is known as the process in which the endometrium is being prepared for pregnancy via cellular changes.
If there is no pregnancy, the corpus luteum degenerates and disappears because it no longer has any role.
Corpus Luteum and the IVF Cycle
In an IVF treatment, the maturing follicles are removed from the ovaries during the egg retrieval procedure. Removal of the follicles from the ovaries means there will be no follicular remnant in the ovaries if the IVF cycle results in a positive outcome. This is because the follicles are removed from the ovary in the process of obtaining viable eggs. Consequently, IVF pregnancies will not have the support of corpus luteum in preparing the endometrium for pregnancy. This is why patients are supplemented with additional progesterone until the end of the first trimester. At the end of the first trimester, the placenta becomes capable of taking over progesterone production, so there is no further need for either the corpus luteum (in natural pregnancies) or external progesterone supplementation in IVF pregnancies.
So, that, in a nutshell, is why external progesterone is given once the follicles have been removed from the ovaries during the oocyte pick-up procedure.
Dr. Ahmet Ozyigit,
MD, MSc Clinical Embryology, PgDip Endocrinology
Patient Coordination whatsapp line: +90 548 885 8000