The most important factor in the reduction of fertility is the age of the woman as, with the passing of the years, there is a reduction in the proper functioning of the ovaries and the reserve of eggs. In addition, the eggs are not as healthy and the risk of miscarriage and foetal malformation is increased. This reduction is further accentuated after the age of forty.

Ovarian cause

• Lack of ovaries (congenital or acquired) : Tumour, infections, etc.  
• Early menopause
• Ovulation problems
• Endometriosis
  
  

Fallopian tubes cause

• Lack of fallopian tubes.
• Total obstruction. .
• Functional disorder: Strength and transport alteration both affecting sperm and egg.
• Fertilized egg nutrition and transport to the uterine cavity.

Uterine cause

Difficulty in the normal development of the embryo.

Cervical cause

Impedes or makes it difficult for the sperm to enter the female genitals through the cervix.

Immune system cause

Existence of anti-sperm antibodies.

Other

• Extreme obesity.
• Anorexia nervosa.
• Toxic substance consumption (heavy use of drugs, medicines, alcohol, tobacco, etc).
• Other diseases (Thyroid disorders).
• Endometriosis.
• Stress.

Mixed causes

• Coinciding factors of both male and female origin.
• Sterility of unknown origin.