Female fertility obeys a complex mechanism. Anything that can alter the production of an oocyte, prevent the meeting between this oocyte and the sperm or interfere with the implantation of the egg can stop this mechanism and prevent one from becoming pregnant. The causes of female infertility are therefore multiple. Here are the main ones.

Ovulation disorders are the leading cause of female infertility. Ovulation, which occurs normally in each cycle, is an essential step in pregnancy. Without it there is no fertilizable oocyte, and therefore no fertilization possible.

Different elements can disrupt this physiological process and lead to dysovulation (abnormal or rare ovulation) or anovulation (absence of ovulation): hormones, conductors of the ovarian cycle, the very structure of the ovaries, the ovarian follicle stock , etc. In question, various pathologies:

Polycystic ovary syndrome (PCOS)

Also called ovarian dystrophy, PCOS is an endocrine pathology characterized by an abnormal accumulation, during the follicular phase, of numerous follicles which do not continue to grow, resulting in dysovulation or anovulation. With a prevalence of 11,9% to 17,8% in women of reproductive age (1), PCOS is one of the most important causes of female infertility.

Hypogonadism of high origin

The hypothalamic-pituitary axis, which governs the secretion of hormones (LH and FSH) that cause ovarian cycles, can function poorly in different situations:

• a deficiency in gonadoliberin (GnRH), a neurohormone that stimulates the secretion of FSH and LH. This deficit is observed in certain genetic abnormalities, such as Kamann-De Morsier syndrome;
• a prolactin pituitary adenoma, a benign tumor of the pituitary gland which causes hyperprolactinemia (excess secretion of prolactin) causing dysovulation;
• a general disease such as kidney failure, liver failure or hypothyroidism can also be the cause of hyperprolactinemia with consequences on fertility;
• certain treatments (psychotropic drugs, anti-depressants, tranquilizers, opiates, etc.) can also lead to hyperprolactinemia;
• emotional shock, sudden weight loss, intensive sporting activity can also have an impact on the hypothalamic-pituitary axis and lead to transient ovulatory disorders.

Ovarian failure

The ovaries no longer work or not, which leads to anovulation. This ovarian failure, sometimes called hypogonadism of low origin (in the ovaries) may be due to:

• a chromosomal abnormality, such as Turner syndrome where one of the X chromosomes is missing;
• treatment (chemotherapy, radiotherapy) or surgery that has impaired ovarian function;
• early menopause: in some women, the ovarian follicle stock is depleted early. The cause can be genetic or autoimmune, but often it remains unexplained.

Endometriosis is characterized by the presence of tissue of the uterine lining outside the uterus (ovaries, tubes, outer wall of the uterus, vagina, etc.). This tissue behaves like that of the endometrium: under the effect of hormones, it bleeds during menstruation. This blood cannot be evacuated, it stagnates and can cause inflammation, lesions, adhesions, cysts. Depending on their degree and location, these lesions can damage the tubes, interfere with the proper functioning of the ovaries, prevent implantation. Thus in 15 to 20% of cases, endometriosis is associated with infertility.

After ejaculation in the vagina, the sperm must pass through the cervix, the first obstacle to be overcome on their way to reach the oocyte. The cells of the cervix secrete a mucus called cervical mucus, the properties of which vary during the cycle to promote the passage of sperm (at the time of ovulation) or on the contrary to hinder it. Any pathology that alters the cervical mucus in quantity, quality or pH can prevent the passage of sperm, and therefore fertilization. In question :

• an infection ;
• an abnormality of the endocervical glands leading to a secretion disorder;
• following treatment of the cervix to remove pre-cancerous lesions (contribution).

The tubes are the other important place of passage for the sperm, which must go up them in order to reach the oocyte which waits in the upper part of a tube. If the tubes are blocked, sperm cannot pass and there can be no fertilization. Sometimes the tubes are not blocked but damaged, and the mucous membrane that lines them can no longer properly play its role of propelling the fertilized egg towards the uterus, which increases the risk of ectopic pregnancy.

Salpingitis (infection of the tubes) is the most common cause of tubal abnormalities. It can follow a sexually transmitted infection (chlamydia, gonococcus), more rarely a gynecological examination or medical procedure (abortion, curettage, insertion of an IUD).

A problem with the uterus can prevent implantation of the fertilized egg. It can be:

• a uterine synechia, that is to say the more or less extensive joining of the walls of the uterus. These scarring lesions are due to infection following surgery or a procedure in the uterus (curettage, termination of pregnancy);
• fibroids or polyps which may, depending on their size and location, prevent implantation or deform the uterus and block the tubes;
• a congenital or acquired uterine malformation, following treatment such as Distilbene®. Taking this drug, prescribed to some women until 1977 to prevent miscarriages, caused genital abnormalities in some women exposed in utero.
• endometritis (infection of the endometrium)

Finally, remember that apart from any pathology, certain factors influence natural fertility:

• age: female fertility decreases after 30 years. The chances of pregnancy in each cycle are 25% at 25, 12% at 35, 6% at 40 (2). In addition, after 40 years, the risk of miscarriage is doubled;
• being overweight, obese or thin;
• tobacco, alcohol;
• intensive sport.