To become any kind of doctor, students must pass four years of medical school and complete an internship. If medical students want to specialize in a certain area, they must complete both medical school and a four-year residency in a particular field. To become a doctor of OB/GYN (O-B/G-Y-N), this residency training must be in the field of obstetrics and gynecology. After passing a written exam, completing a two-year practice, and passing an oral exam, the student officially becomes an OB/GYN. To become Board Certified in Reproductive Endocrinology, the doctor must successfully complete the requirements for board certification in OB/GYN as well as a two- to three-year fellowship in reproductive endocrinology, pass a written exam, finish a two-year practice, and then pass a three-hour oral exam. If doctors are practicing in reproductive endocrinology, but haven't completed the oral exam, they're considered Board Eligible in Reproductive Endocrinology. About 800 (eight hundred) doctors are board eligible, while about 500 (five hundred) are board certified. Some doctors might not be certified in infertility, but can still have expertise in the field. Some urologists specialize in andrology, and can deal with most aspects of male infertility. They've completed a two-year fellowship and passed an exam in andrology.