Etiology

Female causes
Tubal disorders such as blocked fallopian tubes which can be secondary to untreated sexually transmitted infections (STIs), complications of unsafe abortion, PID or abdominal/pelvic surgery.
Uterine disorders which can be secondary to endometriosis, congenital uterine conditions such as septate uterus, or uterine masses such as fibroids.
Ovarian disorders such as polycystic ovarian syndrome and Ovarian masses, congenital conditions such as ovarian agenesis.
Endocrine disorders causing imbalances of reproductive hormones. It is more pronounced when hypothalamus and the pituitary glands are involved. Examples of common disorders affecting this system include pituitary cancers and hypopituitarism.

Male causes
Ductal system disorders such as obstruction of the reproductive tract causing dysfunctionalities in the ejection of semen. This blockage can occur in the tubes that carry semen (such as ejaculatory ducts and seminal vesicles). Blockages are commonly due to injuries or infections of the genital tract.
Hormonal disorders leading to abnormalities in hormones produced by the pituitary gland, hypothalamus and testicles.
Hormones such as testosterone regulate sperm production. Example of disorders that result in hormonal imbalance include pituitary or testicular cancers.
Testicular failure to produce sperm, for example due to varicoceles or medical treatments that impair sperm-producing cells (such as chemotherapy).
Abnormal sperm function and quality, conditions or situations that cause abnormal shape (morphology) and movement (motility) of the sperm negatively affect fertility. For example, the use of anabolic steroids can cause abnormal semen parameters such sperm count and shape.
Penile dysfunction.