The cause of infertility depends on wether it is male infertility or female infertility. Out of the 6.1 million people affected by fertility problems. About 40% of the cause of infertility is due to female problems, another 40% of is due to male problems and 20% is known as unexplained infertility. This basically means that doctors can not find any fertility problems with either the male or the female.

The Cause of Infertility in Males

In the case of men, the main cause of infertility can be divided as follows:

Deficient Sperm Production- Basically means that the men is not producing enough good quality sperm. Even though it only takes one sperm for conception, the number and quality of sperm in semen is important. A semen test is usually the first male fertility test performed.
Ductal Obstruction- Meaning that the semen is obstructed from reaching the egg.
Ejaculatory Dysfunction- Premature or retrograde ejaculation.
Disorders of the Accessory Glands- These include infection, inflammation or even anti-sperm antibodies.
Coital Disorders- Defects in the technique or erectile dysfunction.

The Cause of Infertility in Females

Here is a review of the most common causes of infertility in women. The fertility problems can be divided as follows:

Ovarian and ovulation problems- Women with an ovulation disorder are said to not ovulate at all or they may ovulate irregularly, compared to the normal ovulation during the 28-day cycle. Other ovarian causes would include the polycystic ovary syndrome (PCOS), ovarian neoplasm, diminished ovarian reserve, luteal dysfunction, premature menopause, Turner syndrome, and so on. Most of these disorders prevent the release of a mature egg from the ovaries, or have hormone imbalances, or produce eggs that become damaged or have chromosomal defects.

Tube or peritoneal causes- This would include Endometriosis or the uterine lining (the endometrial tissue) growing outside the uterus or it is unprepared for egg implantation, blockage of the fallopian tubes which prevents an egg from traveling to the uterus, and many more.

Hypothalamic-pituitary causes -These would include the common hypopituitarism, hyperprolactinemia, kallmann syndrome and other hypothalamic dysfunctions.

Cervical, vaginal and uterine problems- Uterine problems would include problems with the structure of the uterus itself, uterine fibroids which causes congenital anomalies (birth defects) and repeated miscarriages, Asherman's syndrome, or any other uterine malformations. Vaginal Problems would include vaginal obstruction which prevents the sperms to travel to the tubes and vaginismus. Cervical problems would include the side effects of anti-sperm antibodies, insufficient cervical mucus which is needed for the sperm to travel and survive, and cervical stenosis.

Genetic causes- Another cause of infertility which is not as common are genetic causes. These can include androgen insensitivity syndrome, fibroids, and various other conditions.

Cause of Infertility- General Factors

In addition to the causes specified above. Other general health factors can affect a woman's fertility and cause infertility. These general factors are diabetes, thyroid or any defects and disorders of the liver and kidneys.

Depending on the couple, the cause of infertility can be due to the man or the woman. An infertility specialist will usually start with the least invasive test and the most common causes of infertility to diagnose the cause of infertility.