How Sperm Is Made
Sperm production (spermatogenesis) takes place continuously in the testicles, controlled by hormones from the brain (FSH, LH) and testosterone. The full cycle from immature cell to mature sperm takes around 72-90 days. This means that anything affecting sperm health — illness, medication, lifestyle changes — has its biggest effect about 3 months later. Healthy adult men produce 50-100 million sperm per day. A normal ejaculation contains 200-300 million sperm, but only a few hundred reach the egg in the fallopian tube. Quality and quantity both matter for fertility.
What Makes a Healthy Semen Sample
Volume: 1.4 mL or more per ejaculation (WHO 2021 reference)
Concentration: 16 million sperm per mL or more
Total count: 39 million sperm or more per ejaculation
Total motility: 42% or more sperm moving
Progressive motility: 30% or more sperm swimming forward
Morphology: 4% or more sperm with normal shape (using strict criteria)
Vitality: 54% or more live sperm
pH, white blood cells and other markers also assessed
Factors That Affect Male Fertility
Age: Sperm quality gradually declines from around 40-45, with increased DNA damage
Smoking: Reduces sperm count, motility and DNA quality
Alcohol: Heavy drinking reduces testosterone and sperm production
Recreational drugs: Cannabis, cocaine, anabolic steroids all impair fertility — steroids can cause permanent damage
Weight: Obesity is associated with lower testosterone and reduced sperm parameters
Heat: Saunas, hot tubs, tight clothing, laptop on lap — testicles need to be cooler than body temperature
Medical conditions: Varicocele, undescended testicles, infections, hormonal disorders, genetic conditions
Medications: Some antidepressants, blood pressure drugs, chemotherapy and steroids affect fertility
Environmental exposures: Pesticides, heavy metals, certain industrial chemicals
Chronic illness: Diabetes, kidney disease and untreated thyroid problems all matter
When to Get a Semen Analysis
Every couple struggling to conceive should have a semen analysis early in the workup — it is the simplest and most informative test of male fertility. Specifically: after 12 months of trying without conception (6 months if female partner is over 35); before any female fertility testing or treatment; if you have a history of testicular surgery, undescended testicles, varicocele or chemotherapy; if you have very low libido or erectile dysfunction; or before fertility preservation. Two samples taken 4-12 weeks apart give a more reliable picture, as sperm parameters vary naturally. Abnormal results should always lead to specialist referral, not just generic lifestyle advice.