Some infertile couples may experience difficulty in having a baby because of coital difficulty, infrequent intercourse or wrongly timed intercourse. Besides psychological causes, the physical causes are -

Male -

• Damage to the special nerves which cause erection. This could have been the result of an injury, surgery or disease.
• Impotence or erectile dysfunction due to deficient blood flow to the penis .
• Chronic illnesses such as kidney or liver failure and diabetes.
• Side effects of prescribed drugs e.g. certain drugs for lowering high blood pressure.
• Diabetes (30 % of diabetics suffer from some form of sexual dysfunction). 
• Hormonal eg. hyperprolactinemia or low testosterone levels.
• Heavy smoking, alcohol and drug abuse.
• Congenital penile abnormalities

Female -

• Painful scar (e.g. episiotomy) or a vaginal infection causing superficial pain
• Congenital abnormalities such as a tough hymen or unusually narrow entrance.
• Endometriosis when the woman experiences pain deep in her pelvis in the organs that surround the top of the vagina.
• Vaginismus or the inability of the woman to relax her vaginal muscles, preventing penetration by the male.

The term is used when despite thorough investigations no apparent cause for infertility is found. However, possible causes include:

• Defective fimbriae - the fimbriae which are like delicate tentacles at the outer end of the tube are unable to pick up the egg at ovulation. 
• Sperm lacking the fertilizing capacity.
• Defective endometrium which does not allow the embryo to implant.
• The follicle fails to release the egg at ovulation and thus the egg is trapped inside the corpus luteum.
• Psychological stress