Paternal sub-fertility has many causes and contributes to 20-30% of all infertility cases (2). There is evidence suggesting a decrease in the quality of semen over recent decades (5). Causes involve factors that affect spermatogenesis leading to low sperm concentration, poor sperm motility or abnormal sperm morphology (11). These factors can not only decrease the chances of fertilisation leading to infertility but also affect early embryo development if fertility is achieved (12). Despite research, the large majority of causes affecting male fertility remain unknown (2). Poor sperm quality is also associated with failure of implantation, miscarriage, compromised embryonic development that could lead to birth defects, or long term health consequences in the child (12).
Physical and Sexual Factors
Physical factors involve physical barriers to sperm development or blockages of ejaculatory pathways. Varicocele (enlargement of the sperm vessels) is the most common physical factor affecting fertility in men leading to low sperm count and low sperm quality (9). There is some evidence that testicular torsion earlier in life may affect male fertility by decreasing sperm count, however, effects on long term fertility of men and potential to archive pregnancy seem negligible (23). Retrograde ejaculation, where semen is ejaculated in the bladder instead of exiting through the penis is a rare but significant barrier to male fertility (13). The most common sexual problems that can interfere with pregnancy is erectile dysfunction, where the male partner cannot sustain an erection long enough to reach insemination. This is most commonly an early sign of cardiovascular disease where there is a blockage of blood flow to the penis (15). However, there are also psychological causes of erectile dysfunction such as depression and sexual trauma (16).
Genetic factors
The two most commonly observed genetic causes of male infertility are chromosomal aberrations and Y microdeletions (14). Klinefelter’s syndrome XXY is the most common chromosomal disorder leading to infertility in men (14). Y chromosome micro-deletions have been shown to lead to poor sperm mobility and low sperm count (14). Partial deletions and/or duplications of the AZF region on the Y chromosome may also be involved in male infertility however the research is not well established and controversial (14).
Infectious diseases
“Chlamydia trachomatis, Mycoplasma genitalium, hepatitis B, tuberculosis, Streptococcus faecalis, and mumps are found to be associated with male infertility” (18). Furthermore, certain urinary tract infections have been shown to interfere with spermatogenesis through means of inflammation (20).
Hormonal Factors
Imbalances in the HPG (hypothalamic-pituitary-gonadal) axis can lead to compromised male reproductive function (6) Imbalances in GnRH hormone can cause further imbalances in FSH, LH and testosterone production which leads to compromised spermatogenesis (6). Intensified sperm DNA fragmentation was associated with both very high and very low levels of FSH and LH (22). High prolactin hormone in males is also associated with compromised spermatogenesis through inhibition of pulsatile gonadotropin hormones which down-regulates testosterone levels and overall sperm production (7).
Lifestyle and Environmental factors
Higher Exposure to certain environmental chemicals in the workplace including solvents, insecticides, silicones, adhesives and radiation has been shown to negatively affect male fertility (17). High heat exposure is also shown to temporarily affect sperm production (1). Excessive alcohol use has been established to negatively affect sperm morphology and sperm production (8). Smoking is confirmed to interfere with the quality of seminal fluid as well as hinder sperm motility (8). Recreational drugs such as marijuana and cocaine are demonstrated to affect the HPG axis, spermatogenesis and sperm function (19). The use of some pharmaceutical drugs such as SSRI’s and popular hair loss drugs such as minoxidial have demonstrated an increased likelihood of hormonal imbalances, sexual dysfucnrtion and an increase in sperm DNA fragmentation (4). DNA fragmentation is associated with both decreased fertilisation, decreased implantation rates, increased miscarriage rates and issues in early embryo development (4). Poor dietary habits such as eating foods high in saturated and trans fats, refined carbohydrates and meat are associated with poorer semen analysis results when compared to men that regularly consumed higher amounts of fresh fruits and vegetables (21).
Age
There is an association between advanced paternal age and increased likelihood of genetic mutations as well as infertility, miscarriage, birth defects, poor neurodevelopmental outcomes, and childhood cancer (3). Observationally as men age the number of Leydig cells decreases, which leads to lower testosterone levels and a decreased number of type A spermatagonia stem cells. There is also an age-related decrease in the testicular tubular lumen. All these aspects affect the quality of the sperm and increase the risk for abnormal embryo development (10).
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