Infertility can be caused by a number of factors. These could range from stress to malnutrition and age. General health and surroundings also cause infertility. Infertility is not to be confused with impotency which is a completely different thing. It is not a much known factor that like females, males too have a hormonal cycle. A woman may get pregnant during her hormonal cycle but if the male is not in the right stage of his cycle the chances are much lower. The female cycle covers 28 days but the male cycle has not yet been mapped out.
The man cycle has no fixed indicators and does not match his hormonal cycle. A male can release sperm whenever he wishes to, but the quality of the sperm may not be good, diminishing his ability to impregnate. The only sure way to determine a man's fertility is to get tested. In females, an irregular pattern of her periods could indicate infertility. However this is not a sure indicator as irregular periods could be symptom of a number of other health hazards. Again the best way to know is to get tested.
Health is an issue in fertility as well. If a woman is underweight or overweight her fertility is affected. A woman needs to be at or around her ideal body weight. The right hormonal balance needs to be maintained. If the woman is on a rich diet the hormonal cycle is thrown off. If the woman is undernourished the hip region becomes too narrow and her ability to conceive babies suffers. Drinking can also lead to sterility. Alcohol consumption causes a woman to become infertile for a considerable length of time. Alcohol consumption needs to be totally eliminated if a woman desires to get pregnant. However sterility due to alcohol and barrenness are two different things.
There are several other causes of infertility in women. If the woman has a cyst in her ovaries can prevent a woman from getting pregnant. A twisted ovary can prevent the egg from descending into the fallopian tube and making it difficult for the sperm to travel to the egg. Judging infertility in a man is much more difficult. Health does not seem to play a role in it. A skin guy has as much change of getting a lady pregnant as a heavily muscled one. The only thing sure is that fertility goes down with an increase in obesity and age.