The veins draining the testicle also cool the artery feeding it, keeping it a couple degrees below body temperature, which sperm production needs. In a varicocele the one-way valves fail and warm blood pools backward. The resulting heat and stagnation build up oxidative stress that damages sperm DNA and drags down the cells that make testosterone ¹. Around 8 or 9 in 10 sit on the left, a plumbing quirk.

Having one is common; being harmed by one is not. Varicoceles turn up in about a third of men with primary infertility and up to four in five with secondary infertility ². Repair reliably improves the semen numbers, concentration and motility, and cuts the share of sperm with broken DNA ^{3 4}.

Whether that makes babies is genuinely contested. The strongest single trial found spontaneous pregnancy in a third of treated men versus an eighth of observed men over a year ⁵, but pooling trials shrinks or erases the benefit ⁶, and Cochrane rated the evidence very low quality ⁷. The honest read: a real but moderate boost in the right man, and no fertility play outside that group.

Beyond fertility, three smaller reasons it matters. Repair nudges testosterone up by about 35 to 100 ng/dL, enough to move low-normal toward mid-range but nothing like testosterone therapy ⁸. In teenage boys it can stunt the affected testicle; a 20% size gap is the usual surgical threshold, and earlier repair recovers more volume ⁹. And 2 to 10 percent get a dull scrotal ache that worsens with standing, which microsurgery relieves in four of five well-selected men ¹⁰.

The decision is narrower than most guides make it sound. The American and European guidelines converge on the same triggers.

To proceed, microsurgical subinguinal varicocelectomy is the gold standard: recurrence under 2%, a week off desk work. Embolization by an interventional radiologist skips the scalpel with equivalent fertility outcomes and a 1-to-3-day recovery ⁷.

The clock, if repair was the right call. The three-month semen analysis usually shows nothing; the sperm cycle takes about that long. Six months is when concentration, motility, and DNA quality tend to improve, in roughly two thirds of treated men ^{3 4}. When a pregnancy comes it lands a median of about seven months out.