This is probably the most common of the causes for infertility in men. Sperm are very fragile and most don't make their trip through the woman's system. This is why most men produce millions of them at a time, however, the less a man produces, the less chances he'll have to be able to impregnate a woman.

The only way to get an accurate sperm count for a man is to be tested at a doctor's office. The amount of ejaculate or size of a man's genital organs have nothing to do with actual sperm count.

Certain lifestyles, like increased alcohol intake and smoking, can also have a negative effect on sperm count and are some of the most common causes for infertility. Men who are 40 or older often have decreased fertility.

Low sperm motility

This is a problem commonly referred to as 'slow' or 'sluggish' sperm. The sperm do not move as well as they should and so do not make the entire journey through a woman's system in order to fertilize the egg. This is also one of the most common causes for infertility in men.

For Women

There are many causes for infertility and reproductive issues for women, from simple reasons to those that are more complicated. Here are the most common:

Anovulation.

This refers to a lack of ovulation, or release of eggs from the ovary. The major cause of anovulation is a condition called polycystic ovary disease, or PCOS. This is the most common of the causes for infertility in women.

The fallopian tubes and endometriosis.

Another of the causes for infertility is the inability of the fallopian tubes to carry eggs from the ovary to the uterus, usually due to scar tissue or a condition called endometriosis. Endometriosis is a condition where tissue similar to the lining of the uterus (the endometrial stroma and glands, which should only be located inside the uterus) is found elsewhere in the body. Endometriosis lesions can be found anywhere in the pelvic cavity: on the ovaries, the fallopian tubes, and on the pelvic sidewall.

For Both Men and Women

Age is one of the major causes for infertility in both men and women. In women, fertility declines with age, and even more so after the age of 35. Conception after age 45 is possible but rare.

Obesity is also one of the causes for infertility for both men and woman. Many studies have also begun to link a man's excessive body weight with his inability to produce healthy sperm. Cholesterol is damaging to his sperm count and breaks down the health of the sperm that is present.