Azoospermia is defined as the absence of spermatozoa in the semen. It is due to a blockage in the channels (obstructive azospermia-OA) that carry the sperm out from the testes or the lack of sperm production (nonobstructive azospermia-NOA). In OA the testicles are of normal size and hormone levels (FSH and inhibin) are normal. In cases of OA a genetic disorder called cystic fibrosis can be present that can be determined by a genetic mutation survey. If there is a genetic mutation in the man, the woman should also be checked. If both are carriers, the baby will have the risk of having cystic fibrosis. In this circumstance preimplantation genetic diagnosis should be couples with the IVF treatment. In men with OA spermatozoa can be easily retreved either from the epididymis (PESA) or the testes (PTSA) with needle aspiration. The spermatozoa thus retrieved can be used for microinjection.

In azoospermia due to deficient sperm production in the testes (NOA), either there is no sperm left or production is done at very few foci. From this point of view surgical exploration of the testes either by conventional means or under the operating microscope is necessary. Viable spermatozoa that can be used for microinjection can be retrieved from approximately 50% of men with NOA. Men with NOA may carry chromosomal defects the most common being Klinefelter sydrome (47 XXY). Approximately 10% of men with NOA will have microdeletions (deleted gene sequences) on their Y chromosome. If this is the case microdeletions will pass on to future generations of male offspring.

There is no chance of getting pregnant other than microinjection in patients with azoospermia. In azoospermia due to blockage sperms could be collected with a needle (PESA/PTSA). In azoospermia due to production abnormality, sperms are collected from the testis by open surgery and this procedure is called TESE. Although sperms can be found in all men with azoospermia due to blockage, in azoospermia due to production abnormality sperm is found in every other man.