The best thing to do is to ask your doctor/clinic about their policy on confidentiality BEFORE you share anything with them you would not like your parents to know.
A doctor should be able to directly answer your questions about what they will/will not share with a parent or guardian. If you're not happy with their answer, find another service that will respect your privacy.
Services that cater to young people are excellent. Also, telling a doctor the full truth about your life - including your sexual activity - only means you will get more accurate and appropriate services. [ alisonmarie's advice column | Ask alisonmarie A Question ]
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