Hypogonadism: failure to produce enough testosterone due to hormonal imbalances, causing reduced or no spermatogenesis to occur. There are two types of hypogonadism: primary (the brain is secreting FSH and LH normally, but testosterone just isn't being made) and secondary (the brain isn't making GnRH and/or LH and FSH that is needed to produce testosterone). And not enough testosterone = not enough sperm production. Testosterone replacement therapy may be able to supplement the inadequate amount of testosterone inside the body to stimulate sperm production. However, this needs to be discussed with a healthcare provider due to some serious potential side effects.
Cryptorchidism: failure of the teste(s) to descend from the abdomen and into the scrotum during fetal development. This can hinder sperm development since normal body temperature is too high for sperm production. Surgical correction (orchiopexy) can reposition the teste(s) in the scrotum so normal sperm production can occur.
Vasectomy: surgical removal of part of the vas deferens. One stop on the sperm's journey is through the vas deferens, so removing part of this tube and sealing it closed creates a barrier for sperm transport during an ejaculation. It's possible to have a vasectomy reversed (cut 2 more pieces of the vas deferens and seal them together so the sperm can complete their natural journey) or sperm can be collected from either the testes or epididymis through surgeries known as TESEs (TESAs) or MESAS.
Erectile Dysfunction: the inability to initiate and/or maintain an erection. There are multiple reasons that this can occur, and it ultimately hinders normal ejaculation from occurring. Medications known as PDE inhibitors may help men with erectile dysfunction, but, again, this needs to be discussed with a healthcare provider.
Andropause (male menopause): a decline in testosterone production that can occur as males reach ~40 years of age. The exact cause of andropause is unknown, but it's theorized that less testosterone production causes less sperm production. Of note, sperm DNA also tends to become more abnormal as men age. Testosterone replacement therapy can help combat the lower levels of testosterone to increase sperm production.
Varicocele: a varicose vein in the testicle(s), which can hinder sperm production because the increased blood flow to the vein increases the temperature in the testicles (which we know can affect sperm production). Varicoceles can be removed via corrective surgery, which may be required if fertility is at risk.
Retrograde Ejaculation: semen flows backwards into the bladder instead of into the urethra (and out through the tip of the penis) during an ejaculation due to the bladder neck muscle not closing properly. There are some medications that may help the bladder neck muscle close normally. Talk to your doctor to learn more.
Azoospermia: no normal, viable sperm are found in an ejaculate. There are multiple causes for this, including blockages in the sperm's pathway (from inflammation, infection, or trauma) or abnormalities in the testicles that prevent sperm production from occurring (increased temperature, hormonal imbalance). Treatment depends on what is causing the issue. In some cases, a TESE (TESA) or MESA surgery may be required to retrieve sperm from the epididymis or testicles.
Genetic Disorders: abnormalities in the cullular DNA that can lead to decreased/no sperm production and/or transport. An example of this is Klinefelter's Syndrome, in which males have an extra X chromosome (more on this later) that causes them to be infertile. Another example is cystic fibrosis, which causes sperm to be produced but unable to move through the male reproductive tract. Treatment for these disorders depends on their nature, though sometimes there is no known cure and donor sperm may need to be considered.
Other Causes: sometimes infertility has no known cause (unexplained), and sometimes lifestyle factors can cause infertility. For example, there could be a lot of sperm that are abnormal or have low motility due to tobacco use and/or chemotherapy. Treatment depends on the diagnosis.
There are many other causes of male infertility, but these highlight some of the more common causes and possible treatment options. If you or your partner believe that you may be infertile, talk with your doctor about possible options moving forward.