No matter what specialty you choose, it will take years to become a physician. The three phases of medical training after you finish high school include undergraduate or college education, medical school and graduate medical education, which could involve a residency or a residency plus a fellowship. The minimum for almost all specialties is 12 years, but there are some differences for those who choose to become OB-GYNs and pediatricians.

About the Specialties

OB-GYNs -- the initials stand for obstetrician-gynecologist -- treat women at all stages of life, with a focus on the female reproductive system. This specialty combines medical management, surgery, pregnancy and childbirth. OB-GYNs can also specialize in areas such as gynecologic oncology -- working with women with cancer of the reproductive tract -- or infertility. Pediatricians focus on children and specialize in all aspects of care for children and adolescents. Pediatric specialties include pediatric heart doctors, or cardiologists, pediatric oncologists and neonatologists, who care for sick or premature newborns.

College

All physicians begin their education with a four-year college degree. Most choose a Bachelor of Science or Bachelor of Arts, either in a basic science field or with a strong emphasis on sciences, according to the American Medical Association, or AMA. Most medical schools expect an aspiring physician to complete basic biology, genetics, microbiology, molecular biology, basic chemistry, organic chemistry, physics and calculus, according to YourPediatrician.com. Volunteering while at college will also increase your chances of getting into medical school. During your junior or senior year in college, you must also complete the Medical College Admissions Test, or MCAT.

Medical School

Graduating from medical school gives you a doctor of medicine or a doctor of osteopathy degree, according to the AMA. Either takes four years. In the first two years of medical school, the focus on basic sciences continues, but narrows specifically to the human aspects, such as human anatomy. You will study topics such as physiology, chemistry, microbiology, pharmacology and neuroanatomy. The second two years are the beginning of actual hands-on clinical experience in areas such as cardiology, surgery and radiology. This is the point at which most physicians choose specialties such as pediatrics or OB-GYN.

Residency

The next step for the fledgling physician is residency. Residency is when the paths of an OB-GYN and pediatrician begin to diverge. Residencies vary by specialty and last three to seven years. OB-GYNs spend a minimum of four years in residency. Those who choose a subspecialty may go on for another one to three years of additional training. A pediatric residency is usually three years, but again, those who want to specialize need two to four years of fellowship training. The shortest training period for an OB-GYN is 12 years and the shortest for a pediatrician is 11 years.