Infertility can be caused by many different factors and, in 30% of couples, a cause cannot be identified.

Infertility in women

Ovulation disorders

Infertility is most commonly caused by problems with ovulation (the monthly release of an egg). Some of these problems stop women releasing eggs at all, and some cause an egg to be released during some cycles, but not others. Ovulation problems can occur as a result of a number of conditions that are outlined below.

• Premature ovarian failure - when your ovaries stop working before the age of 40.
• Polycystic ovary syndrome (PCOS) - a condition which makes it more difficult for the ovaries to produce an egg.
• Thyroid problems - both an overactive and an underactive thyroid can prevent ovulation.
• Chronic conditions - if you have a debilitating condition, such as cancer, or AIDS, it can prevent your ovaries from releasing eggs.

Womb and fallopian tubes

The fallopian tubes transport an egg from the ovary to the womb, where the fertilized egg will grow. If the womb, or fallopian tubes , become damaged, or stop working,then it may be very difficult to conceive naturally. This can occur following a number of procedures, or conditions, as outlined below.

• Pelvic surgery - this can sometimes cause damage and scarring to the fallopian tubes .
• Cervical surgery - this can sometimes cause scarring, or shorten the cervix (neck of the womb).
• Submucosal fibroids - are benign (non cancerous) tumors that develop in the muscle underneath the inner lining of the womb, and may prevent implantation.
• Endometriosis - this is a condition where cells, normally found in the womb lining, start growing on other organs. This can cause adhesions in the pelvis and limit the movement of the fimbria (tiny fronds at the end of the fallopian tubes ) which direct the egg into the tube.
• Previous sterilization - some women choose to be sterilized if they do not wish to have any more children. Sterilization involves blocking the fallopian tubes to make it impossible for an egg to travel to the womb. This process is rarely reversible. If you do have a sterilization reversed, it will not necessarily mean that you will become fertile again.

Medicines and drugs

The side effects of some types of medication, and drugs, can affect your fertility. These medicines are outlined below.

Non-steroidal anti-inflammatory drugs (NSAIDs) - long-term use, or a high dosage of NSAIDs, like ibuprofen or aspirin, can make it more difficult to conceive.

Chemotherapy - the medicines used with chemotherapy can sometimes cause ovarian failure, which means your ovaries will no longer be able to function properly. Ovarian failure can be permanent.

Illegal drugs - drugs such as marijuana, and cocaine, can seriously affect your fertility, making it more difficult to ovulate. They may also adversely affect the functioning of your fallopian tubes .

Age

Infertility in women is also linked to age. Women in their early twenties are about twice as fertile as women in their late thirties. The biggest decrease in fertility begins during the mid thirties.

Infertility in men

Semen

The most common cause of male infertility is abnormal semen (the fluid ejaculated during sex that contains sperm). Abnormal semen accounts for 75% of male infertility cases, and the cause of abnormal semen is often unknown. Semen can be abnormal for a number of reasons which are outlined below.

• Decreased number of sperm - you may have a very low sperm count, or have no sperm at all.
• Decreased sperm mobility - if you have decreased sperm mobility, it will be harder for your sperm to swim to the egg.
• Abnormal sperm - sometimes sperm can be an abnormal shape, making it harder for them to move and fertilize an egg.

Many cases of abnormal semen are unexplained, but there are several factors which can affect semen and sperm.

Testicles

The testicles are responsible for producing and storing sperm. If they are damaged, it can seriously affect the quality of your semen. This may occur if you have:

• an infection of your testicles ,
• testicular cancer, or
• testicular surgery.

Ejaculation disorders

Some men have a condition which makes it difficult for them to ejaculate. For example, retrograde ejaculation, causes you to ejaculate semen into your bladder . The ejaculatory ducts can also sometimes become blocked, or obstructed, and this too can make it difficult to ejaculate normally.

Medicines and drugs

• Sulfasalazine - this is an anti-inflammatory medicine used to treat conditions such as Crohn's disease ( inflammation of the intestine) and rheumatoid arthritis (painful swelling of the joints ). This medicine can decrease your number of sperm. However, its effects are only temporary, and your sperm count should return to normal when you stop taking it.
• Anabolic steroids - these steroids are often used illegally to build muscles and improve athletic performance. Long term use, or abuse, of anabolic steroids can reduce your sperm count and sperm mobility.
• Chemotherapy - the medicines used with chemotherapy can sometimes severely reduce the production of sperm.

Factors that affect both men and women

There are a number of factors which can affect fertility in both men and women. These include:

• Weight - being overweight, or obese, reduces both male and female fertility. In women, it can affect ovulation. Being underweight can also impact on fertility, particularly for women, who will not ovulate if they are severely underweight.
• Sexually transmitted diseases (STDs) - there are several STDs which can cause infertility. The most common is chlamydia, which can damage the fallopian tubes in women and cause swelling and tenderness of the scrotum (pouch of skin containing the testes) in men.
• Smoking - not only does smoking affect your general and long term health, it can also affect fertility.
• Occupational and environmental factors - exposure to certain pesticides, metals and solvents can affect fertility in both men and women.
• Stress - if either you, or your partner, are stressed, it may affect your relationship. Stress can reduce libido (sexual desire), therefore reducing the frequency of sexual intercourse. Severe stress may also affect female ovulation and can limit sperm production