Doing a specialization is a choice of that particular individual.If you want a career in teaching field then post graduation is a must.But doing a specialization will surely enhance your career opportunities and depending on where you complete your studies and where you want to practice medicine also determines the scope of specialization. Refer this link for further information
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No it is not compulsory to do MD or MS after MBBS. It is purely based on one's own interest. If you want to specialize in a particular area then i suggest that you pursue higher studies, as nowadays people prefer to go to a specialist.
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