Causes of infertility

The causes of infertility are many and varied. They are classified as either absolute or relative. Absolute causes of infertility will, in the absence of treatment, totally prevent pregnancy. Relative causes reduce the chance of pregnancy but do not necessarily prevent it all together. An analogy is that absolute causes are like turning the pregnancy switch off and relative causes are similar to turning the dial down.

Over the last thirty years the impact of changing attitudes towards pregnancy, childbirth, work and family commitments has electively lead to a marked increase in the age of first pregnancy. As a result of these changes in western societies there is no doubt that increasing female age has become the single most important influence on a couples chance of achieving a pregnancy. For most couples it is a more important influence on the chance of successful pregnancy than any specific cause and it is becoming a more and more common problem as couples decide to start families later in life.

Among the specific causes of infertility there are however only four absolute causes of infertility that without treatment totally prevent pregnancy. They are:

• No sperm

• No eggs

• Blockage preventing egg and sperm meeting

• Prevention of embryo implantation

Often however a series of relative causes multiply together to reduce the chance of pregnancy by such an amount the realistic impact on couples is as severe as if they had an absolute cause.


Female factors

There are several main areas where fertility can be jeopardized in the female: the ovaries, the fallopian tubes, the uterus, and the hormones affecting these.

There will be a decrease in fertility if:

• ovulation is irregular or absent – this can be corrected with hormone treatment in most cases
• there is an obstruction between the vagina and the ovary, preventing the sperm and egg from meeting. These usually occur in the fallopian tubes, and it was for this condition that in vitro fertilization (IVF) was originally developed. Obstructions can often be treated surgically, but generally success rates are better with IVF
  
• there is an abnormality of the uterus, such as polyps or fibroids (obstructions can often be treated surgically, but can return) which impairs embryo implantation into the lining of the uterus
• endometriosis which is a common condition where tissue like the lining of the uterus grows outside the uterus, hampering a number of events leading to a pregnancy
  

Male factors

Male fertility seems less complicated than female fertility simply because the male is responsible for fewer stages in the process of creating a baby. Essentially, male fertility comes down to sperm.

There will be a decrease in fertility if the sperm are:

• not being produced in adequate numbers (or at all)
• being produced, but facing an obstruction that prevents them from reaching the outside world
• being produced, but not swimming very well
• stimulating antibody production in either partner by causing an allergic reaction.
  

Some of these problems can be treated surgically, but in most cases IVF is the best option.


Unexplained infertility

The cause of infertility is not always obvious. In many cases, both partners can appear to be fine, but they can’t seem to get pregnant. This is known as unexplained infertility. Having no identifiable cause does not mean that there is no available treatment. Indeed the prospect of spontaneous pregnancy is often higher than for those couples with a specific cause. Indeed IVF is highly effective for couples with female age under 40 years who have unexplained infertility.