Select the option that can be used as a one-word substitute for the given group of words.
"The doctor who deals with the female reproductive system."

Let's check the fields of specialization for each doctor:
* Gynaecologist: A physician or surgeon qualified to practice gynecology, dealing with the functions and diseases specific to women and girls, especially those affecting the reproductive system.
* Orthodontist: A dentist who is qualified to treat irregularities of the teeth and jaws.
* Cardiologist: A doctor who specializes in the study or treatment of heart diseases and heart abnormalities.
* Ophthalmologist: A specialist in the branch of medicine concerned with the study and treatment of disorders and diseases of the eye.