A complete absence of sperm (spermatozoa) in the semen. Detectable only by performing a sperm count, as semen looks the same whether it contains sperm or not. Due either to an obstruction (usually in the epididymis or vas deferens), and called obstructive azoospermia, or to failure of sperm to form or to mature in the testis (called maturation arrest). See also spermatogenesis and testicular sperm extraction (TESE).

Azoospermia caused by low sperm production rates in the testis, including maturation arrest. Can often be overcome with testicular sperm extraction (TESE) followed by in vitro fertilisation utilising intracytoplasmic sperm insertion (ICSI).

An absence of semen despite male orgasm; thus, different to azoospermia, an absence of sperm.

Taking a small sample of tissue for diagnosis under the microscope. Biopsies of the endometrium can be done without anesthetic, through the cervix (see premenstrual biopsy). Biopsies of the ovary or of the lining of the peritoneal cavity (e.g. to detect subtle endometriosis) are done at laparoscopy. A testicular biopsy is done to determine why there's azoospermia. Using microscopic techniques, even an early embryo can be biopsied

Congenital (present from birth) absence of the two vasa deferentia, which conduct sperm from the testes to the ejaculate; hence a cause of obstructive azoospermia. Because the vas deferens is usually affected on both sides, the word "bilateral" is often inserted, as CBAVD. Infertility is inevitable, but can be overcome using in vitro fertilisation with testicular sperm extraction. The cause, however, is usually the presence among the man's genes of one of the serious alleles for the genetic disease cystic fibrosis (which, having recessive inheritance, results when there are two such alleles present); it can also come about when there are one or two of the less serious abnormal alleles for this condition. The more common of the abnormal alleles should therefore be screened for (using a specially set up polymerase chain reaction on white blood cells): should an abnormal allele be present (delta F508 is the most common seriously abnormal one), the woman should be screened too, to predict the chance of cystic fibrosis occurring in the offspring.

A serious genetic disease (with a recessive inheritance pattern) characterised by a major disturbance of the body's mucus secretions, and thus a cause of incapacitating disease of the lungs. Important in our context because the heterozygous (or carrier) state in men can manifest with azoospermia due to congenital absence of the vasa deferentia -- the infertility of which is nowadays able to be overcome with testicular sperm extraction and ICSI, thus risking inadvertent transmission.

A trisomy with a karyotype of 47,XXY -- i.e. a male with an extra X-chromosome. A cause of azoospermia.

Strictly, oligozoospermia, meaning a reduced number of sperm cells (spermatozoa) in the ejaculate (compared with azoospermia, which means no sperm in the ejaculate). More generally, a decrease in normal, motile sperm, and more or less encompassing laborious terms such as 'asthenozoospermia' (weak motility) and 'teratozoospermia' (abnormal sperm), and even more laborious ones, such as 'oligoasthenoteratozoospermia', which do not reward the effort of concocting them.

(ROSNI) Experimental form of testicular sperm extraction (TESE) followed by intracytoplasmic sperm insertion (ICSI) in which the nucleus of a round (very immature) spermatid is isolated for injection into the egg (or secondary oocyte). Intended to be used in treating non-obstructive azoospermia with severe maturation arrest, when more spermatozoa are not obtainable. Animal studies show higher pregnancy rates than with round spermatid injection (ROSI), but limited studies in humans still indicate very high rates of embryopathy. Not recommended clinically.

In women, when measured during menstruation, inversely related to the serum FSH (and probably provides no more information than the day 3 FSH level in predicting depletion of eggs); in men with azoospermia, levels predict the likelihood of being able to obtain sperm for ICSI at testicular sperm extraction.

Development of a sperm cell, in the tubules of the testes (the testicular tubules), from spermatogonium and spermatocyte to spermatozoon (the last part of this process, from spermatid to spermatozoon, is called spermiogenesis). The process of spermatogenesis takes 56 days. At any one location in a tubule there are cells at four different stages of maturity, so mature sperm are released from a particular location into the lumen of the testicular tubules every 14 days. A systematic interruption of spermatogenesis results in azoospermia and is called maturation arrest.

The state of absolute infertility or complete infertility, with no chance of getting pregnant without special help. Causes include azoospermia, anovulation (especially primary ovarian failure), and blocked fallopian tubes.

A biopsy of the testis to work out the reason behind an absence of sperm cells (azoospermia). Also used for testicular sperm extraction (TESE).

(TESE) Dissection into the testis itself, in men with azoospermia due to maturation arrest, to recover (by 'teasing out') immature sperm cells from the (often small) fraction of testicular tubules there which still contain such cells. The sperm cells are used for in vitro fertilisation using intracytoplasmic sperm insertion (ICSI).

Vasectomy reversal, the operation for reversing a sterilisation operation (a vasectomy) in a man involving removal of the blocked part of each vas deferens, in the upper part of the scrotum, and joining by microsurgery one cut end or the vas to the other cut end. Generally not as successful at returning fertility as the equivalent operation in women (tubal anastomosis): the development of sperm antibodies increases with the length of time since sterilisation and limits the effective sperm count after the reversal. Many clinics now carry out cryostorage of some sperm obtained at vasectomy reversal so that if pregnancy does not happen, or azoospermia persists, in vitro fertilisation (IVF) can be carried out with ICSI without requiring a later operation (for MESA) on the man. MESA with ICSI and IVF can be used as an alternative to vasovasostomy.