Terms oligospermia, oligozoospermia, and low sperm count refer to semen with a low concentration of sperm and is a common finding in male infertility. Often semen with a decreased sperm concentration may also show significant abnormalities in sperm morphology and motility (technically oligoasthenoteratozoospermia). There has been interest in replacing the descriptive terms used in semen analysis with more quantitative information. Diagnosis
The diagnosis of oligozoospermia is based on one low count in a semen analysis performed on two occasions. For many decades sperm concentrations of less than 20 million sperm/ml were considered low or oligospermic, recently, however, the WHO reassessed sperm criteria and established a lower reference point, less than 15 million sperm/ml, consistent with the 5th percentile for fertile men. Sperm concentrations fluctuate and oligospermia may be temporary or permanent. Sources usually classify oligospermia in 3 classes:
Mild: concentrations 10 million – 15 million sperm/mL
Moderate: concentrations 5 million – 10 million sperm/mL
Severe: concentrations less than 5 million sperm/mLThe diagnosis of oligozoospermia requires a work-up via semen analysis (listed in Male infertility). Causes
There are many causes for oligospermia including:

Pre-testicular causes
Pre-testicular factors refer to conditions that impede adequate support of the testes and include situations of poor hormonal support and poor general health including:

Hypogonadism due to various causes
Drugs, alcohol, smoking
Strenuous riding (bicycle riding, horseback riding)
Medications, including androgens. Testicular factors
Testicular factors refer to conditions where the testes produces semen of poor quality despite adequate hormonal support and include:

Age
Genetic defects on the Y chromosome
Y chromosome microdeletions
Abnormal set of chromosomes
Klinefelter syndrome
Neoplasm, e.g.
A common single-nucleotide polymorphism of BRCA2 is associated with severe oligospermia.Men with mild oligospermia (semen concentration of 15 million to 20 million sperm/ml) were studied for an association of sperm DNA damage with life style factors. A significant association was found between sperm DNA damage and factors such as age, obesity and occupational stress. Treatment
Treatment takes place within the context of infertility management and needs also to consider the fecundity of the female partner. Thus the choices can be complex. In a number of situations direct medical or surgical intervention can improve the sperm concentration, examples are use of FSH  in men with pituitary hypogonadism, antibiotics in case of infections,  or operative corrections of a hydrocele, varicocele, or vas deferens obstruction. In most cases of oligospermia including its idiopathic form there is no direct medical or surgical intervention agreed to be effective. Empirically many medical approaches have been tried including clomiphene citrate, tamoxifen, HMG, FSH,  HCG, testosterone, Vitamin E, Vitamin C, anti-oxidants, carnitine, acetyl-L-carnitine, zinc, high-protein diets. In a number of pilot studies some positive results have been obtained. Clomiphene citrate has been used with modest success. The combination of tamoxifen plus testosterone was reported to improve the sperm situation.The use of carnitine showed some promise in a controlled trial in selected cases of male infertility improving sperm quality and further studies are needed.In many situations, intrauterine inseminations are performed with success.