Still not pregnant after a year of trying?

Stress

Most women who haven't fallen pregnant quickly become emotional and anxious. This can become a vicious circle, with stress and worry leading to a further delays in getting pregnant. Try to relax, it will increase your chances of getting pregnant.

Sperm problems

These are the largest single identifiable cause for infertility, accounting for about 24% of cases in couples trying to get pregnant. Sperm problems can be due to drugs such as beta-blockers, alcohol, tobacco and cannabis. Infections like mumps can occasionally lead to a permanently low sperm count. More often, low sperm counts are due to an unexplained failure of the sperm-producing cells in the testicle.

Problems with ovulation

Ovulation failure accounts for about 21% of cases of infertility. This is often suspected when periods are irregular, infrequent or very light. Underlying causes of ovulation failure include:

• Eating disorders such as anorexia nervosa
• Low body weight and low body fat in athletes
• Premature menopause
• Polycystic ovary sdyndrome (PCOS). In this condition the ovulation failure may be associated with obesity, acne and hirsutism (excess facial or body hair)
• Thyroid problems
• Over-production of a hormone called prolactin by the pituitary gland.

Blockage of the Fallopian tubes

This accounts for about 14% of cases of infertility. The most common underlying problem is pelvic inflammatory disease (PID). This is most often as a result of sexually transmitted infection, particularly chlamydia and gonorrhoea.

Chlamydia infection is currently the most common cause of blocked tubes in young women. It is estimated that 10% of all sexually active young women aged 16 to 25 are currently infected with chlamydia, and that about 10% of infected women will become infertile as a result.

Other causes of PID include infection from coils (IUDs), infection following pelvic surgery, and previous peritonitis (inflammation of the lining of the abdomen) from things like a burst appendix.

Endometriosis

This accounts for about 6% of infertility cases. This is a condition where parts of the lining of the womb (endometrium) find their way outside the womb and into the pelvis. This can damage the tubes, but in most cases this isn't the problem. For some unknown reason, even a small amount of endometriosis can interfere with fertility.

Cervical mucus problems

Sometimes there is a 'mismatch' between the woman's cervical mucus and her partner's sperm, which results in the sperm being unable to get through the mucus, or them being killed off before they can swim up into the womb. This is described as 'hostile mucus', which sounds really unpleasant, but is just bad luck. The mucus may not be hostile to a different partner, but that's not much consolation to a couple suffering from this problem.

'Unexplained infertility'

This accounts for about a quarter of all cases of infertility which are investigated. This means that no cause can be found. Some of these couples will eventually get pregnant, simply a lot more slowly than the average. For every couple who conceive in the first month, there are other couples who take years.

Some other couples have problems getting pregnant because of life rhythm incompatibility, with husbands working away from home and limited amounts of time together. They may have very enthusiastic sex when they get together, but if it's at the wrong time of the month, then nothing happens.

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• Secondary fertility