How common is male infertility, and what are its causes?

Infertility is defined clinically in women and men who cannot achieve pregnancy after 1 year of having intercourse without using birth control, and in women who have two or more failed pregnancies. Studies suggest that after 1 year of having unprotected sex, 15% of couples are unable to conceive, and after 2 years, 10% of couples still have not had a successful pregnancy.^1,2 In couples younger than age 30 who are generally healthy, 20% to 37% are able to conceive in the first 3 months.³

Many different medical conditions and other factors can contribute to fertility problems, and an individual case may have a single cause, several causes, or—in some cases—no identifiable cause. Overall, one-third of infertility cases are caused by male reproductive issues, one-third by female reproductive issues, and one-third by both male and female reproductive issues or by unknown factors.⁴

To conceive a child, a man's sperm must combine with a woman's egg. The testicles make and store sperm, which are ejaculated by the penis to deliver sperm to the female reproductive tract during sexual intercourse. The most common issues that lead to infertility in men are problems that affect how the testicles work. Other problems are hormone imbalances or blockages in the male reproductive organs. In about 50% of cases, the cause of male infertility cannot be determined.⁵

A complete lack of sperm occurs in about 10% to 15% of men who are infertile.⁶ A hormone imbalance or blockage of sperm movement can cause a lack of sperm. In some cases of infertility, a man produces less sperm than normal. The most common cause of this condition is varicocele, an enlarged vein in the testicle. Varicocele is present in about 40% of men with infertility problems.⁷