The quality of evidence is downgraded by study quality and inconsistency (unexplained variability in results).
A Cochrane review included 10 studies with a total of 894 men. All studies included men from couples with subfertility problems. No studies reported live birth. The combined fixed-effect OR of the 10 studies for the outcome of pregnancy was 1.47 (95% CI 1.05 to 2.05), favouring the intervention. The NNT for an additional beneficial outcome was 17. The outcome of the subgroup analysis excluding men with normal semen analysis and subclinical varicocele (five studies) favoured treatment, with a combined OR 2.39 (95% CI 1.56 to 3.66). The NNT for an additional beneficial outcome was 7.