Sperm Volume and pH The lower limit of normal semen volume is 1.5 mL or more and the pH should be 7.2 or higher. These parameters are affected mainly by the balance between the acidic secretions of the prostate gland and the alkaline ﬂuid from the seminal vesicles. Low volume along with pH less than 7 suggests obstruction of the ejaculatory ducts or absence of the vas deferens. Difficulties with collection, retrograde ejaculation, or androgen deficiency can contribute to low volume. High volumes greater than 5 mL suggest inﬂammation of the accessory glands (30).
Sperm Concentration Sperm concentration or density is defined as the number of sperm per milliliter in the total ejaculate. The normal lower limit is 15 million/mL or more, recently revised from 20 million/mL or more (30,43). Only intact sperm are counted in determining sperm concentration. Fifteen percent to 20% of infertile men are azoospermic (no sperm) and 10% have a density of less than 1 million/mL (30,47).
Sperm Motility and Viability Sperm motility is the percentage of progressively motile sperm in the ejaculate. The normal lower limit is 32% or more, recently revised from 50% or more (30,43). Viability should be at least 58%. Progressive motility refers to movement either linearly or in a large circle regardless of speed. Nonprogressive motility describes sperm that display only small movements or twitching or no movement at all (immotile). Assessments of speed of progression, either rapid or slow, have been removed from the revised guidelines because of difficulty in unbiased measurement of this parameter. A reduction in sperm motility is referred to as asthenozoospermia. Leukocytes can impair sperm motility through oxidative stress. When a large number of immotile sperm are present or when progressive motility is less than 40%,
Differential Diagnosis of Male Factor viability studies should be performed. Viable immotile sperm may have ﬂagellar defects, while the presence of nonviable immotile sperm (necrozoospermia) suggests epididymal pathology. Viable sperm have intact plasma membranes, which will not stain (dye exclusion) but will swell in hypoosmotic solutions (hypoosmotic swelling test) (30).
Sperm Morphology Morphology refers to anatomic malformations of the sperm. The lower limit for normal morphology is 4% or more using strict criteria, a change from previous guidelines using a more lenient assessment and a cutoff of 30% or more (30,43). Assessment of sperm morphology involves fixing and staining of a portion of the specimen. The strict Tygerberg criteria were introduced by Kruger et al. in 1986 to assess sperm morphology (30,48,49). Using this system, the entire spermatozoon—including the head, midpiece, and tail—is assessed, and even mild abnormalities in head forms are classified as abnormal. Most sperm from normal men exhibit minor abnormalities when subjected to Tygerberg standards. An abnormality of sperm morphology is known as teratozoospermia, and these sperm have poor fertilizing potential and may have abnormal DNA. A disadvantage to any morphology assessment is that reproducibility may be hampered by the subjective nature of the assessment (30).