Testosterone is the key hormone in male reproduction. Similar to female reproduction, the hormones FSH and LH play a critical role. LH causes the testes or testicles to produce testosterone, whereas FSH aids in the production and maturation of sperm.

When ejaculation occurs during intercourse, approximately 100 million sperm are released and must swim through the vagina, cervix, and uterus to meet the egg in the Fallopian tube. Although hundreds of millions of sperm enter the vagina, only a thousand or so make it to the Fallopian tube. This is normal as sperm are the smallest cells in the human body and undergo quite the journey to meet the egg.