What are the most common causes of sterility?


Both sterility and infertility are caused by different factors, which may affect women (female cause), men (male cause) or both members of the couple (mixed cause).

In a given percentage of cases, the sterility factor is not even diagnosed (sterility without diagnosis or with an unknown cause).



Patient’s age
Alterations in menstrual cycle
Premature ovarian failure
Polycystic ovary
Tubular obstruction
Uterine malformations
Recurrent IVF treatment failure
Recurrent miscarriages

Age very much influences a women’s fertility.
When they are born, women have the maximum complement of eggs (oocytes) in their ovaries. The number of these oocytes decreases as they grow older so that when they reach the age of around 50 years old, 80% of women have exhausted their ovarian reserve and thereupon experience menopause.

Female fertility remains stable up to the age of 35, yet from 38 onwards falls considerably while the quality of the oocytes also decreases (increase in the frequency and quantity of chromosomal anomalies that, if fertilised, yield embryos with a low implantation capacity and/or high miscarriage rate).
Evaluation of the woman’s ovarian reserve provides information that is very important for indicating the most suitable treatment.

The ovarian cycle has an essential function in achieving pregnancy.
During the ovarian cycle ovulation occurs and the endometrium is prepared to receive embryos. This lasts 28 days (from 25 to 30 days in most women), while ovulation occurs halfway through the cycle: on day 14, approximately.

Menstrual cycle disorders::

Polymenorrhea: shortening of the menstrual cycle to periods of fewer than 21 days.

Oligomenorrhea: long menstrual cycles of 35 days to 6 months.

Primary amenorrhea: when a woman has never menstruated.

Secondary amenorrhea: absence of menstruation for a period of at least 6 months. It may be caused by polycystic ovary syndrome, eating disorders (anorexia and bulimia), elite sports, hyperprolactinaemia or by genetic abnormalities.

Anovulation: when the oocyte is not released into the Fallopian tubes, either because it has not formed or because it has not matured sufficiently. This disorder may be caused by changes in ovarian hormone levels (estradiol, progesterone), in the hypothalamo-hypophyseal system (GnRH, FSH, LH, prolactin, etc.) or in thyroids (TSH).
Anovulation occurs in 25% of cases and is one of the causes with the best prospects once diagnosis and treatment have been established.

Known also as premature ovarian failure, it is characterised by the premature stoppage of ovarian activity before the woman reaches the age of 40. It affects approximately 1 to 4% of women of fertile age.
Its causes may be genetic (as is the case of Turner's or Fragile X syndrome), hereditary, enzymatic alterations, autoimmune diseases or the result of having undergone chemotherapy or radiotherapy treatments.

Polycystic ovary syndrome (PCOS) is the most common cause of menstrual cycle alterations in women. It occurs in 4 to 7% of women of reproductive age. It is characterised by the presence of two or more of the following circumstances:

  • Irregular cycles associated with ovulation problems.
  • Ovarian morphology with presence of numerous follicles and also often with changes in FSH and LH hormone levels.
  • Excess androgen activity.
  • Anomalies in the metabolism of glucose and insulin.

This condition has a broad variety of manifestations: from women with regular periods and normal physical appearance to more severe cases of absence of menstruation, hirsutism, acne and obesity.

Benign disease that affects many patients of reproductive age. It entails the appearance and growth of endometrial tissue (layer that covers the interior of the uterus) outside the uterine cavity. It most commonly appears in the pelvic cavity (ovaries, Fallopian tubes, behind the uterus, intestines or even in the bladder) and, less often, outside the abdomen.
Although its causes are not fully known, endometriosis is associated with a cause of sterility in 20% of cases.

It occurs when the Fallopian tubes, the tracts in charge of transporting spermatozoa to the egg and taking this to the uterus once fertilised, have some type of lesion, which can be a blockage or an adhesion that stops them from working properly. This leads to a reduction in capacity or total incapacity to become pregnant.
The main causes of tubular obstruction are infectious in origin and caused by germs such as gonorrhoea, Chlamydia, hydrosalpinx (accumulation of liquid in the tubes) or the effects of endometriosis.
Tubular disorders cause 25% of cases of female sterility.

Congenital pathology that affects 5% of the population at large. It occurs mainly because of abnormal development of the müllerian ducts during the formation of the embryo, although it may also be associated with other genital, urological or rectal malformations.
Although there are different uterine malformations, the most common are in the septate uterus and the bicornuate uterus.
The presence of myomata or polyps and the presence of intrauterine adhesions may also affect endometrial receptivity to embryos.

Genetic alterations in the X chromosome, such as deletions or translocations of the X chromosome or abnormal karyotype, such as Turner's syndrome (XO).

These cases in which several unsuccessful in vitro fertilisation (IVF) treatments have been attempted. The most common causes include lack of ovarian stimulation, failed fertilisation or embryo implantation failure.

Recurrent miscarriage patients are those who have suffered two or more premature and spontaneous terminations of pregnancy in the first three months.


Oligozoospermia: reduction in the concentration of spermatozoa in the semen. It is usually caused by scant production of sperm in the testicles, although it may sometimes also be caused by partial obstruction of ducts. Asthenozoospermia: decrease in the progressive motility of spermatozoa. The origin may be testicular, epididymal, or the action of chemical, infectious or immunological components. Teratozoospermia: low percentage of spermatozoa with a normal morphology. Its origin is mainly testicular or genetic.
These alterations commonly appear in association and oligoasthenoteratozoospermia is the most frequent diagnosis in sterile men.
Azoospermia: this is the most extreme case and entails the absence of spermatozoa in the ejaculate. The causes may be changes in hormone levels (mainly in the hormone FSH), traumatism, infection or for genetic reasons, as is the case of Klinefelter syndrome. It is possible to differentiate between:     

  • Secretory azoospermia: the testicle does not produce spermatozoa.
  • Obstructive azoospermia: the testicle produces spermatozoa but there is a problem in the ductus deferens or in the epididymis that prevents them from being transported to the urethra.

It is defined as the absence of ejaculation. One specific type involves patients with retrograde ejaculation or, in other words, ejaculation that occurs inwards into the urinary bladder rather that outwards through the urethra. The causes may be psychological, neurological or obstructive.

It entails venous dilatation in the testicles. It may lead to sterility, as it reduces the motility of spermatozoa and increases sperm DNA fragmentation.
Varicocele is common in 15-20% of men and in 40% of infertile men.

Absence of testicle in the scrotum. It is caused by malformation of the genitalia during formation of the foetus. It affects 3% of newborn infants and 30% of prematurely born infants. In the latter case, there is a higher risk of the presence of genetic anomalies that affect spermatozoa.

Difficulty in sexual relations prompts a reduction in reproductive capacity. Impotence or other such incapacities can now be efficiently treated to improve quality of life. In such cases, consultation with an andrologist is recommendable.

Infections of the male reproductive system can cause temporary alterations in semen quality as the action of some pathogenic bacteria may block the transport of spermatozoa from the testicles.

Genetic alterations in the Y chromosome such as the Y-chromosome microdeletions or abnormal karyotype, as is the case of Klinefelter syndrome (47 XXY).


There is a problem of sterility in both members of the couple. This occurs in 20% of sterile couples.


The term “sterility of unknown origin” is applied to those cases in which thorough testing of the couple has not yielded diagnosis of any apparent cause of sterility.
Approximately 10 to 15% of sterile couples belong to this group.

The following factors also influence the decrease in fertility:

  • Environmental and professional factors such as continuous exposure to chemical or toxic substances (lead, ethylene oxide, pesticides, etc.) or certain medical treatments such as X-rays and cancer treatments.
  • Factors associated with daily routine habits such as diet, exercise and the consumption of tobacco, alcohol or other drugs.