About half the sperm in any ejaculate are all of the same size and appearance and are referred to as ‘normal morphology’ (morphology just means shape). The other half are all different sizes and shapes and are referred to as ‘abnormal morphology’ because they probably do not take part in fertilisation (although they may have another function). Occasionally a man’s ejaculate contains a higher proportion of abnormal sperm and this is associated with reduced fertility. There are many causes – injury, varicose vein of the scrotum (varicocoele) and some drugs, but in the majority of cases no cause is found. In these cases there is no way of improving the sperm before it is ejaculated and treatment is with artificial insemination (IUI) or, more commonly, IVF.