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Today, one in six couples require referral for investigation and treatment for infertility.

Natural conception is dependent upon several factors and processes.  Firstly, the woman needs to produce an egg from one of her ovaries which must be able to travel freely down into the fallopian tube.  Secondly, the man has to produce a high number of good quality sperm which are capable of making the journey from the vagina, through the cervix and into a fallopian tube where fertilisation takes place.  The timing of sexual intercourse is also crucial as conception can only occur during ovulation (ie when the female produces an egg).  Once fertilisation has occurred, a normal uterus is required in order for the embryo to implant and develop. 

Natural human fertility is low compared with most other species and peak human fertility (defined as the chance of pregnancy per menstrual cycle in the most fertile couples) is no higher than 33%.  However, most fertile couples should achieve pregnancy within a year of regular intercourse.  This rises to 95% over a two year period.

For some couples, therefore, a long delay in conceiving reflects low fertility rather than infertility.  Even so, the usual criterion to define infertility and initiate investigations, is a delay of more than one year.  This is especially true for patients over 30 when the natural decline in fertility begins to accelerate.

In addition to the age factor, the main causes of infertility are sperm dysfunction, ovulation disorder and fallopian tube damage.

About 17% of couples will have more than one cause for their infertility.  It is therefore important to make complete investigations from the outset rather than focusing treatment on the first cause identified.  In just under 20% of couples no definite cause will be found, even after complete investigation.  These couples are said to have ‘unexplained infertility’ but can, of course, still be treated.