When it comes to conception, there is no disputing the fact that the male is 50% of the equation. Not surprisingly for 50% of couples having trouble getting pregnant, male infertility is the reason.

To find the cause of male infertility a physician (fertility specialists are typically reproductive endocrinologists, but many couples will also consult a urologist or start with their family physician) will take a thorough medical history, do a physical exam, and get a semen sample. A semen analysis checks for several key factors including their sperm shape (morphology — specifically, each sperm should have one oval head, a normal midsection, and one tail), number (60-80 million per milliliter is preferred, but 20 million/ml is considered the normal threshold), motility (movement — 50%-60% should be motile). The amount of semen (ejaculate) is critical — 1.5 to 5 milliliters is considered normal. Too much or too little semen can reduce the chance of conception. It may sound precarious, but remember it only takes one sperm to successfully unite with an egg in order for you to start picking out baby names.

Male infertility may be due to a varicocele, which is a dilated, or swollen, vein in the testicle. It’s assumed that the varicocele raises the temperature in the testicle thereby lowering the sperm count. Temperature is critical with sperm. Overheating can impair production and motility. Other infertility culprits include inherited disorders that cause abnormal development of the testicles, or a testosterone deficiency (male hypogonadism). Signs of hypogonadism include a low sex drive, limited sexual development, even reduced hair growth on the face and body.

Infections may harm sperm motility or interfere with their travels. Sexually transmitted diseases, such as chlamydia and gonorrhea can cause scarring that blocks the vas deferens (the tube that carries sperm from the testicles to the penis) or the epididymis (the sperm warehouse). Prior surgeries can also leave scar tissue. Infections can also lead to inflammation of the urethra (urinary tube) or prostate (a gland involved in producing seminal fluid) and harm sperm production.

Getting a childhood disease, such as the mumps after puberty can adversely impact fertility. Erectile dysfunction, premature ejaculation, not to mention anti-sperm antibodies that target and disable sperm may cause male infertility. Diseases such as diabetes, celiac disease, kidney disease, cirrhosis, sickle cell anemia, cystic fibrosis, multiple sclerosis can also play a role.

Lifestyle causes should always be considered. Smoking, overindulging in alcohol, drug use (e.g. cocaine, marijuana, and anabolic steroids), obesity, malnutrition, and certain medications (e.g. antibiotics, antihypertensives) can adversely impact fertility. Spending a lot time in hot tubs raises testicle temperature, as can sitting for long periods or wearing tight clothing, all of which temporarily reduces sperm production. And then there’s age. Fertility in men, as in women, decreases significantly after 35.

Stress alone can cause infertility by interfering with the hormones needed for proper sperm production. Simply trying to conceive can strain a relationship, and this type of stress can actually cause or exacerbate male infertility. Environment must also be considered. Exposure to toxins such as lead, heavy metals, pesticides, x-rays, radiation and chemotherapy can also hamper male fertility.

With the causes of male fertility this varied it’s essential to be evaluated by a physician. If you’re under age 35 and have been trying to conceive for over a year, or if you’re over 35 and have been trying for six months it’s time to bring in a medical expert. Many causes of male infertility can be successfully treated with medication, surgery or lifestyle changes.

For more information visit, the male fertility section of the American Society of Reproductive Medicine (ASRM).