Causes of male infertility can roughly be categorized as abnormalities of sperm production or sperm function or obstruction of the ductal outflow tract.
During evaluation of a male infertility patient, the basics of male reproductive physiology should be understood. Analogous to the ovary, testes have two functions: the generation of mature germ cells (sperm) and the production of male hormones, primarily testosterone. The seminiferous tubules contain developing sperm and support cells called Sertoli cells or sustentacular cells (see Fig. 19-4). The Sertoli cells form tight junctions that produce a blood-testis barrier. This avascular space within the seminiferous tubules protects sperm from antibodies and toxins but also makes these cells dependent on diffusion for oxygen, nutrients, and metabolic precursors. Located between the seminiferous tubules are Leydig cells, also called interstitial cells, which are responsible for steroid hormone production. In simplistic terms, Leydig cells are similar to the theca cells of the ovary.
Unlike the ovary, testes contain stem cells that allow ongoing production of mature germ cells throughout a male’s life. In a fertile male, approximately 100 to 200 million sperm are produced each day (Sigman, 1997). The process begins with a diploid (46,XY) spermatogonial cell, which grows and becomes a primary spermatocyte. The first meiotic division produces two secondary spermatocytes, and completion of meiosis results in four mature sperm with a haploid (23,X or 23,Y) karyotype. During this developmental process, most sperm cytoplasm is lost, mitochondria that provide energy are positioned in the sperm midpiece, and sperm flagella develop.
Production of sperm requires approximately 70 days. An additional 12 to 21 days is needed for sperm to be transported into the epididymis. Here, they further mature and gain motility (Heller, 1963; Hinrichsen, 1980; Rowley, 1970). Importantly, due to this prolonged developmental period, the results of a semen analysis reflect events during the past 3 months, not a single point in time.
To fertilize an oocyte, human sperm must undergo a process known as capacitation. Capacitation results in sperm hyperactivation (an extreme increase in movement) and the ability to release acrosomal contents, which allow penetration of the ovum’s zona pellucida.
Normal spermatogenesis is dependent on high local levels of testosterone. LH from the anterior pituitary gland stimulates production of testosterone by the Leydig cells. FSH increases LH receptor density on the Leydig cells, thus indirectly contributing to testosterone production. In addition, FSH increases production of sex hormone-binding globulin, also called androgen-binding protein. Androgen-binding protein binds testosterone and maintains high concentrations of this hormone in the seminiferous tubules (Sigman, 1997).
In addition to hormone levels, testicular volume often reflects spermatogenesis, and a normal volume is between 15 and 25 mL. Most of this volume is provided by the seminiferous tubules. Thus, decreased testicular volume is a strong indicator of abnormal spermatogenesis.
Spermatogenesis is directed by genes on the Y chromosome. Autosomal genes also provide important contributions, which continue to be elucidated. Therefore, genetic abnormalities may adversely affect this process, as discussed later.
Male fertility likely decreases modestly with increasing age. Several studies have demonstrated that pregnancy rates decline and time to conception lengthens as male age increases. Studies of semen parameters across age suggest that sperm concentration is maintained, however, sperm motility and morphology progressively worsen (Levitas, 2007). The clinical significance of this change is unclear (Kidd, 2001). In short, although advancing male age may lower fertility, it is probably insignificant compared with aging changes in women.
This is a core test in male fertility evaluation. For this test, the male is asked to refrain from ejaculation for 2 to 3 days, and a specimen is collected by masturbation into a sterile cup. If masturbation is not an option, then a couple can use specially designed Silastic condoms without lubricants. Importantly, the sample should arrive in the laboratory within an hour of ejaculation to allow for optimal analysis.
The sample undergoes liquefaction, or thinning of the seminal fluid, due to enzymes from the liquid contribution of the prostate gland. This process takes 5 to 20 minutes and allows more accurate evaluation of the sperm contained in the seminal fluid. Ideally, two semen samples separated by at least a month are analyzed. In practice, frequently only a single sample is analyzed if parameters are normal.
The reference values for the semen analysis are shown in Table 19-8. A clinician should remember several critical aspects of this test. First, semen characteristics vary across time in a single individual. Second, semen analysis results, particularly morphologic interpretation, differ between laboratories. Thus, reference ranges for the laboratory being used should be known. Note that the concept of “reference” range is more appropriate than “normal” range. Although total motile sperm count correlates with fertility, not all males with “normal” semen parameters display normal fertility (Guzick, 2001). Conversely, patients with semen analysis results outside the reference range may achieve pregnancy. The lack of absolute predictive value for this test is likely due to the fact that it does not provide information regarding sperm function, that is, the ultimate ability to fertilize an oocyte.
TABLE 19-8Semen Analysis Reference Limits ||Download (.pdf) TABLE 19-8 Semen Analysis Reference Limits
|>1.5 mL a |
>15 million/mL a
<1 million/mL b
<5 million/mL b
Most semen analysis reports will indicate semen volume, pH, and presence or absence of fructose. Nearly 80 percent of semen volume comes from the seminal vesicles. Seminal fluid is alkaline and is thought to protect sperm from acidity in prostatic secretions and in the vagina. Seminal fluid also provides fructose as an energy source for sperm. An acidic pH or lack of fructose is consistent with obstruction of the efferent ductal system (Daudin, 2000).
Of parameters, low semen volume often simply reflects incomplete specimen collection or short abstinence interval. However, it may indicate partial vas deferens obstruction or retrograde ejaculation. Partial or complete vas deferens obstruction may be caused by infection, tumor, prior testicular or inguinal surgery, or trauma. Retrograde ejaculation follows failed closure of the bladder neck during ejaculation and allows seminal fluid to flow backward into the bladder. Retrograde ejaculation is suspected in men with diabetes mellitus, spinal cord damage, or prior prostate or other retroperitoneal surgery that may have damaged nerves (Hershlag, 1991). Medications, particularly β-blockers, may contribute to this problem. A postejaculatory urinalysis can detect sperm in the bladder and confirm the diagnosis. If urine is properly alkalinized, these sperm are viable and can be retrieved to achieve pregnancy.
Sperm counts may be normal, or males may have low sperm counts (oligospermia), or no sperm (azoospermia) (Sharlip, 2002). Oligospermia is defined as a concentration less than 15 million sperm per milliliter, and counts below 5 million per milliliter are considered severe. The prevalence of azoospermia is approximately 1 percent of all men. Azoospermia may result from outflow tract obstruction, termed obstructive azoospermia, such as that which occurs with congenital absence of the vas deferens, severe infection, or vasectomy. Azoospermia may also follow testicular failure (nonobstructive azoospermia). In the latter case, careful centrifugation and analysis may identify a small number of motile sperm adequate for IVF use. Alternatively, this latter group may have viable sperm obtainable through either epididymal aspiration or testicular biopsy. As described later, endocrine and genetic evaluation is indicated for men with abnormal sperm counts.
Sperm movement is also assessed, and decreased sperm motility is termed asthenospermia. Some laboratories will distinguish between rapid (grade 3 to 4), slow (grade 2), and nonprogressive (grade 0 to 1) movement. Total progressive motility is the percentage of sperm exhibiting forward movement (grades 2 to 4). Asthenospermia has been attributed to prolonged abstinence, antisperm antibodies, genital tract infections, or varicocele. To differentiate between dead and nonmotile sperm, a hypoosmotic swelling test can be performed. Unlike dead sperm, living sperm can maintain an osmotic gradient. Thus, when mixed with a hypoosmotic solution, living, nonmotile sperm with normal membrane function swell and coil as fluid is absorbed (Casper, 1996). Once identified, these viable sperm may be used for intracytoplasmic sperm injection.
Abnormal sperm morphology is termed teratospermia or teratozoospermia. Kruger and colleagues (1988) developed a detailed characterization of normal sperm morphology, which showed improved correlation with fertilization rates during IVF cycles. Their criteria require careful analysis of the shape and size of the sperm head, the relative size of the acrosome in proportion to the head, and characteristics of the tail, including length, coiling, or presence of two tails. Significantly decreased fertilization rates are seen when normal morphology of the sample falls below 4 percent.
Round cells in a sperm sample may represent either leukocytes or immature sperm. White blood cells (WBCs) can be distinguished from immature sperm using various techniques, including a myeloperoxidase stain for WBCs (Wolff, 1995). True leukocytospermia is defined as greater than 1 million WBCs per milliliter and may indicate chronic epididymitis or prostatitis. In this scenario, many andrologists consider empiric antibiotic treatment prior to obtaining a repeat semen analysis. A common protocol would include doxycycline at a dosage of 100 mg orally twice daily for 2 weeks. Alternative approaches include culture of any expressible discharge or of the semen sample.
Unless a general obstetrician-gynecologist has developed a particular interest and expertise in the area of infertility, persistent abnormal semen analysis findings are an indication for referral to an infertility specialist. Although the partner may be referred directly to a urologist, it may be more reasonable to refer the couple to a reproductive endocrinologist, as the female will also require evaluation. Treatment is likely to be more complex in these couples and will typically be directed to both partners. The reproductive specialist can determine the need for further referral of the male partner to a urologist for investigation of a genetic, anatomic, hormonal, or infectious abnormality.
During the past 10 years, interest in elevated sperm DNA fragmentation as a cause of male factor infertility has increased (Sakkas, 2010; Zini, 2009). Although some degree of DNA damage is likely repaired during embryogenesis, the location and extent of damage may lower fertilization and increase miscarriage rates. Increased levels of DNA damage are associated with advanced paternal age and external factors such as cigarette smoking, chemotherapy, radiation, environmental toxins, varicocele, and genital tract infections. Studies have observed increased levels of reactive oxygen species in sperm samples with abnormal DNA fragmentation rates. In response to this observation, dietary supplementation with the antioxidants vitamin C and vitamin E has been proposed. However, data are currently lacking regarding the efficacy of this approach.
Numerous tests are currently available to analyze for DNA integrity and include the Sperm Chromatin Structure Assay (SCSA), the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, the single-cell gel electrophoresis assay (COMET), and the sperm chromatin dispersion test (SCD) (American Society for Reproductive Medicine, 2013c). Each of these tests provides semiquantitative data on DNA structure. For example, the SCSA is based on the increased susceptibility of DNA with single-strand or double-strand breaks to denature in weak acid. The TUNEL assay exploits the ability of labeled nucleotides to intercalate into DNA breaks for subsequent measurement. These tests are currently hampered by a lack of consensus regarding appropriate threshold values and by conflicting data regarding their ability to predict successful pregnancy. As a result, currently evidence is insufficient to recommend the routine use of these tests in infertile couples. Nevertheless, the concept that sperm DNA integrity can be adversely affected through multiple mechanisms provides useful insight into a previously underappreciated cause of male infertility.
Antisperm antibodies may be detected in as many as 10 percent of men. However, controversy exists regarding the negative fertility effects of antisperm antibodies found in semen. These antibodies may be particularly prevalent following vasectomy, testicular torsion, testicular biopsy, or other clinical situations in which the blood-testis barrier is breached (Turek, 1994). Treatment historically included corticosteroids, but it is unclear if this approach improves fertility. Moreover, significant side effects, including aseptic necrosis of the hip, have been reported in treated patients. Current data suggest that antisperm antibody assay does not need to be a routine component of infertility evaluation.
Numerous assays have been developed to test sperm function. These include the mannose fluorescence assay, hemizona assay, sperm penetration assay, and acrosome reaction test. The predictive significance of these assays is questionable, as they are based on highly nonphysiologic conditions and results vary widely from infertility center to infertility center. Most are no longer used and are not considered part of a basic infertility evaluation.
Hormonal Evaluation of the Male
Hormonal testing in the male is analogous to endocrine testing in an anovulatory female. In overview, abnormalities may be due to central defects in hypothalamic-pituitary function or due to defects within the testes. Most urologists will defer testing unless a sperm concentration is below 10 million/mL. Testing will include measurements of serum FSH and testosterone levels.
Low FSH and low testosterone levels are consistent with hypothalamic dysfunction, such as idiopathic hypogonadotropic hypogonadism or Kallman syndrome (Chap. 16). In these patients, sperm production may be achieved with gonadotropin treatment. Although such treatment is frequently successful, at least 6 months may be required for detection of sperm production.
Elevated FSH and low testosterone levels provide evidence of testicular failure, and most men with oligospermia fall into this category. In this patient group, it is important to determine, based on testosterone levels, whether testosterone replacement is indicated. Normal spermatogenesis requires high levels of intratesticular testosterone, which cannot be achieved with exogenous testosterone. Furthermore, many of these men will lack spermatogonial stem cells. Thus, testosterone replacement will not rescue sperm production. In fact, replacement will decrease gonadotropin stimulation of remaining testicular function through negative feedback at the hypothalamus and pituitary. Unless the couple has chosen to use donor sperm, androgen supplementation is deferred during fertility treatment. However, replacement will provide other benefits, such as improved libido and sexual function, maintenance of muscle mass and bone density, and a general sense of well-being.
Additional hormonal testing may be included as part of an evaluation of the infertile male. Elevated serum prolactin levels and thyroid dysfunction affect spermatogenesis and are the most likely endocrinopathies to be detected (Sharlip, 2002; Sigman, 1997).
Genetic Testing of the Male
Genetic abnormalities are a relatively common cause of abnormal semen characteristics (American Society for Reproductive Medicine, 2008a). Approximately 15 percent of azoospermic men and 5 percent of severely oligospermic men will have an abnormal karyotype. Although genetic abnormalities cannot be corrected, they may have implications for the health of the patient or their offspring. Therefore, karyotyping is pursued when indicated by poor semen analysis results. The lower limit in sperm concentration for such testing varies between practitioners but lies between 3 and 10 million sperm per milliliter.
Klinefelter syndrome (47,XXY) will be a frequent finding. Klinefelter syndrome is observed in approximately 1 in 500 men in the general population and accounts for 1 to 2 percent of male infertility cases. Classically, these men are tall, undervirilized, and have gynecomastia and small, firm testes (De Braekeleer, 1991). As the phenotype varies widely, lack of these characteristics does not preclude chromosomal evaluation. Conversely, a clinician may strongly consider obtaining karyotype testing in any male with these characteristics. Autosomal abnormalities will also be found in a subset of men with severe oligospermia.
A patient with severely decreased sperm counts and a normal karyotype is offered testing for microdeletion of the Y chromosome. Up to 15 percent of men with severe oligospermia or azoospermia will have small deletions in a region of the Y chromosome termed the azoospermia factor region (AZF). If the deletion is within the AZFa or AZFb subregions, then it is unlikely that viable sperm can be recovered for use in IVF. Most men with an AZFc deletion will have viable sperm at biopsy. However, these deletions should be presumed to be inherited by their offspring. The clinical significance of microdeletions in the recently identified AZFd region is unknown, as these patients have apparently normal spermatogenesis (Hopps, 2003; Kent-First, 1999; Pryor, 1997).
Obstructive azoospermia may be due to congenital bilateral absence of the vas deferens (CBAVD). Approximately 70 to 85 percent of men with CBAVD will have mutations found in the cystic fibrosis transmembrane conductance regulator gene (CFTR gene), although not all will have clinical cystic fibrosis (Oates, 1994; Ratbi, 2007). Conversely, essentially all men with clinical cystic fibrosis will have CBAVD. Fortunately, testicular function in these men is usually normal, and adequate sperm may be obtained by epididymal aspiration to achieve pregnancy through IVF. Careful genetic counseling and testing of the female partner for carrier status is critical in these situations.
Evaluation of a severely oligospermic or azoospermic male may include either open or percutaneous testicular biopsy to determine whether viable sperm are present in the seminiferous tubules (Sharlip, 2002). For example, even men with testicular failure diagnosed by elevated serum FSH levels may have adequate sperm on biopsy for use in intracytoplasmic sperm injection. The biopsy specimen can be cryopreserved for future extraction of sperm during an IVF cycle. However, freshly biopsied specimens are generally felt to provide higher success rates. Thus, the biopsy may have diagnostic, prognostic, and therapeutic value.