In some circumstances, a man’s ejaculate may contain very few healthy sperm or even no healthy sperm at all. This is referred to as azoospermia or oligospermia/cryptozoospermia. Reasons for this include
• an inoperable blockage, severing or lack of the vas deferens or
• an extremely reduced sperm production or no sperm production at all – for example caused by genetic defects, environmental toxins, infections, an undescended testicle during childhood that was treated too late or by varicose veins of the testes.
Furthermore, it may be the case that a man cannot ejaculate, for example due to a tumour or because of paraplegia. In such cases, pregnancy by natural means is usually not possible.