Follicular atresia, more commonly known as decreased ovarian reserve, corresponds to the decrease in the number of follicles present in the ovaries. If this phenomenon is natural, it can also be favored by certain factors, in particular genetic or environmental.
Definition: what is the phenomenon of follicular atresia?
The ovaries of mammals constitute the reserve of oocytes. Almost 99% of primordial follicles that begin to grow die during growth. This degeneration is called follicular atresia or follicular atresia. The causes of this natural selection are not yet well understood, and the stimulating and inhibiting factors remain a mystery. This large-scale waste of germ cells caused by follicular atresia occurs throughout the life of the female. We speak of follicular atresia, or decrease in ovarian reservewhen the stock of follicles decreases at an unexpected age, with a risk of inducing conception difficulties for the woman.
What is the cause of follicular atresia?
“While the causes of follicular atresia remain poorly understood, there are very real risk factors, including: menopause premature of genetic origin occurring at 20 or 30 years; karyotype abnormalities; cytogenetic abnormalities of the sex chromosomes which can cause either a complete deficit – we then speak of ovarian insufficiency – or a partial deficit of reduction in the ovarian reserve, responsible for a lower quality of ovarian functioning. Of the unknown environmental phenomena cannot be excluded“, says Professor Philippe Touraine, head of the department of endocrinology and reproductive medicine at the Pitié Salpêtrière hospital.
When does follicular atresia start?
The stock of follicles is built up from intra-uterine life, then it gradually decreases, until menopause. On average, a woman has 5 million during fetal life, 1 to 2 million at birth, and 400,000 at puberty. The follicles naturally begin to atrophy and then gradually disappear from the age of 35. “Other factors can precipitate this process: chemotherapy, radiotherapy, environment. Ovarian reserve is determined by anti-mullerian hormone (AMH) levelsmeasured by a simple blood test, most often during a fertility check-up“, specifies the head of the department of endocrinology and reproductive medicine at the Pitié Salpêtrière hospital.
What is the role of follicular cells?
During a menstrual cycle, the woman recruits several dozen follicles. There is one which will become dominant and which, at the time of ovulation, will release an oocyte. If it meets a sperm, they will form an embryo and then a baby. “In other words, the follicle has a dual function : it is the source of production of sexual gametes and the source of production of hormones (estrogens and progesterone). A woman with follicular atresia is less likely to have good ovulatory quality because she will produce less estrogen to stimulate ovulation. Menopause represents the physiological pattern where there are no more follicles”, develops the specialist.
What if follicular atresia does not occur?
“Follicular atresia always occurs. The age of menopause may be delayed but there are no cases of a woman having been in a menstrual cycle until her death”, explains Professor Philippe Touraine.
Thanks to Pr Philippe TOURAINE, head of the department of endocrinology and reproductive medicine at the Pitié Salpêtrière hospital