A low sperm count or absence of sperm in semen may indicate a problem with the Y chromosome, in particular Y chromosome micro deletion. Other genetic conditions include Klinefelter syndrome and Kallmann syndrome.
Cryptorchidism is a condition where one or both of the testicles are not found in the scrotum, but instead lie in the abdomen. It is also known as an 'undescended testicle'. Some men may also be born without testicles, a condition called 'anorchia'.
This is a condition where the sperm ducts of a male do not develop properly. Sperm is not carried from the testicles to become part of semen, resulting in azoospermia. It is linked with cystic fibrosis.
Use of illegal drugs, alcohol and smoking are all risk factors for reduced fertility.
Many men experience erectile dysfunction. This means they are unable to attain an erection and cannot have penetrative sex needed to conceive. Other men experience problems with ejaculation.
Men who previously had a vasectomy (an operation to make him sterile and prevent pregnancy) will experience what is called obstructive azoospermia.
A varicocoele is a swollen vein on a man's scrotum.
History of a sexually transmitted infection, mumps or inflammation of the testicles may cause infertility.
Chronic disease such as diabetes and high blood pressure, exposure to radiation, high temperatures, and treatment with chemotherapy are all linked with infertility.