Causes of infertility
 
Causes of Female Infertility Causes of Male Infertility
Ovulatory Disorders   Sperm Production Disorders
Fallopian Tube Damage   Anatomical Abnormalities
Endometriosis   Immunological Factors
Cervical/Uterine Factors   Defective Delivery of Sperm
Causes of Female and Male Infertility

Causes of Female Infertility
Several problems can contribute to female infertility; however, the most common causes of infertility in women are:
ovulatory disorders, Fallopian tube damage, endometriosis, cervical/uterine factors.
1: Ovulatory Disorders
These are usually the most common cause of infertility. Infrequent menstruation (oligomenorrhea) or the lack of menstruation (amenorrhea) can serve as an indication of ovulatory disorders. However, even women with regular periods may have an ovulatory disorder. Ovulatory disorders result in problems with the process of ovulation, or the release of the egg from the ovary at specific time intervals. In order for pregnancy to occur, a single sperm must fertilize the egg. Therefore, if ovulation does not occur (annovulation) or if it is irregular and/or infrequent, it can be impossible or extremely difficult to achieve pregnancy. Hormonal imbalances, Polycystic Ovarian Syndrome (PCOS), diminished ovarian reserve, and ovarian cysts can all contribute to ovulatory disorders.

Normal Ovary and Ovarian Cyst
     
  PCO Ovary   PCO Ultrasound  
2: Fallopian Tube Damage
In order for fertilization to occur, the sperm must travel through a Fallopian tube in order to reach the egg. Furthermore, a fertilized egg must be able to travel along the Fallopian tube to the uterus so that implantation can take place. Therefore, if the Fallopian tubes are partially or completely occluded (blocked), fertilization and pregnancy cannot occur. Fallopian tube occlusion can result from Pelvic Inflammatory Disease (PID), endometriosis, adhesions due to surgery, ectopic pregnancies, and sexually transmitted diseases (STDs).
     
  Tubal and Pelvic Adhesions After PID   Occluded Fallopian Tube  
3: Endometriosis
Endometriosis is a condition in which endometrial tissue, which normally lines the uterus, grows outside of the uterus and causes internal bleeding during menstruation that culminates in painful adhesions. These endometrial lesions can then block the Fallopian tubes, impede the movement of the tubes, and impair ovulatory function.
     
  Endometriotic Lesions on Pelvic Wall   Ovarian Endometriotic Cyst  
4: Cervical/Uterine Factors
Anatomical problems with the cervix, cervical infections, and unfavorable cervical mucus can possibly impede fertility. Problems with the uterus that can contribute to infertility include uterine polyps, uterine fibroids, and severe scarring of the uterine wall.
     
  Uterine Fibroids   Endometrial Polyp  
Causes of Male Infertility
The most common causes of male infertility are disorders affecting the production of sperm, anatomical obstructions, immunological factors, and defective delivery of sperm into the female genital tract.
1: Sperm Production Disorders
Sperm production disorders are the most common cause of infertility in men, and tend to affect the quality and quantity of sperm produced. There are several factors that can affect sperm production, such as infectious diseases, endocrine disorders, varicocele (or varicose veins in the scrotum), immunological disorders, environmental factors (e.g. pollution, stress), radiation, and cancer treatments. In the majority of cases no obvious cause is found.
     
  Mature and Immature Sperms   Normal and Abnormal Semen Analysis  
2: Anatomical Abnormalities
Anatomical abnormalities of the male genital tract can affect fertility since they may partially or completely block the expulsion of semen. The abnormality could have been present from birth, or it may arise later in life. Several factors can cause obstruction of the male genital tract, such as infection, inflammation, and/or previous surgery.
3: Immunological Factors
Men may suffer from immunological disorders. In some cases, men make antibodies to their own sperm. As a result, the sperm are often not motile and may even agglutinate (or stick together). Both of these factors would be detrimental to fertilization.
4: Defective Delivery of Sperm
The most common causes of this problem are impotence and premature ejaculation.