Cause of Infertility

Trouble-free natural conception is dependent upon several factors and processes. But essentially the female partner must produce an egg from one of her ovaries and the man a high number of good quality sperm to fertilise the egg. Regular intercourse every two or three days throughout the cycle will increase the chances of the sperm and egg meeting up and fertilisation taking place. Once fertilisation has occurred, a normal uterus is necessary for the embryo to implant and develop as a pregnancy.

If any of these processes is compromised at any stage, the chance of spontaneous conception is reduced, or even impossible. So if you’re having problems with fertility - and as many as one in six couples of reproductive age do - then we’ll investigate the possible causes in you and your partner.

We do not apply any selection criteria to the patients we treat and we advise each patient about their chance of success and the possible risks involved. Your chance of conception may be improved by additional treatments before beginning fertility treatment. But the decision to proceed is always yours – and we will do our very best to achieve the result you want.

Multiple causes of infertility

We find that around one in five couples have more than one explanation for their infertility. This might be a sperm problem in the male partner, and hormonal irregularities in the female. In such cases it is important that both causes are treated from the outset. Conversely, we also find that in another 20% of couples no definite cause of infertility can be found, even after a full investigation. However, while these couples are said to have ‘unexplained infertility’, they can still be treated successfully.


Natural human fertility is low compared with most other species and the chance of pregnancy per cycle in the most fertile couples is no higher than 25%. However, the majority of couples (around 90%) should achieve pregnancy within a year of regular intercourse (and 95% over two years). So a long delay in conceiving might simply reflect low fertility rather than infertility.

However, the usual benchmark to define infertility and start investigations is a delay of more than one year. This is especially true for patients aged over 35, when the decline in natural fertility begins to accelerate.