A semen analysis, measuring the volume of the ejaculate, the density of spermatozoa ('sperm cells', or just 'sperm') in it (expressed as so many million sperm per milliliter), the proportion of sperm swimming normally (the motility), and the proportion with a normal shape. A normal sperm count consists of a volume of more than 1 ml; a density of more than 20 million per ml; a motility of more than 50 percent; and normal forms of more than 50 percent (casual examination) or more than 14 percent (critical examination by the strict criteria recently advocated by the World Health Organisation).

An estimate of the percentage of spermatozoa that have an abnormal shape of the head, mid-piece or tail. Part of the routine sperm count.

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).

The quality of movement, especially forward propulsion, shown by sperm cells (spermatozoa) and caused by effective beating of their tail, or flagellum. Analyzed as part of the routine sperm count.

Fluid produced by the male genital tract at ejaculation. Contains spermatozoa, as well as many other substances, including those that make the ejaculate coagulate (and then called a coagulum, which is given time to liquefy before a semen analysis is done on it). Sperm cells account for only about 1 percent of the volume of the ejaculate, so it's not possible to be confident about a man's sperm count just on the basis of the volume of the semen ejaculated.

Formal name for a sperm count.

Infertility for which no obvious cause has been found after the following tests have been done with normal results: a sperm count or postcoital test; a test of ovulation, such as a serum progesterone that is satisfactorily high; and a laparoscopy (used to show that the tubes are open and that there is no endometriosis or other obvious abnormality). Although a hysterosalpingogram (HSG) can substitute for laparoscopy in excluding blockage of the fallopian tubes, an HSG can miss peritubal adhesions and will miss endometriosis. Infertility should not be considered unexplained unless a thorough, careful laparoscopy has been done.

A varicose vein in the scrotum, which in some cases can increase the temperature of the testis, causing oligospermia; more common on the left side than on the right (because the left testicular vein is longer and more likely to have incompetent valves). One of the few treatable causes of male infertility (the treatment is to tie off the vein), although not all sperm counts improve.

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.