Just so you know, your boyfriend could be charged and most likely, convicted, of statutory sexual assault. If an individual enages in consensual sexual conduct with another who is 16 or younger and they are 4 or more years older, they've committed statutory sexual assault.
That being said, I would imagine your boyfriend is not well liked by your parents? Your best bet is to be honest with your parents and level with them. I think the DA will take your relationship with the boyfriend into consideration and may not charge him with a crime. It all depends. If you hide it from your parents, I think there's a stonger likelihood that they will feel more strongly against him. This is a tough call and I don't want to play God with your life. You should consult with local counsel that can discuss this with the police or the DA before it snowballs.
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Getting emancipated will not necessarily solve the problem of statutory rape charges. The state will find out about the child either through a report by your parents, or perhaps from the hospital, although this is less likely.
Try to talk to your parents and get them on your side with the pregnancy and the relationship. This will make them 1. less likely to report the issue, and 2. less likely to ask the District Attorney to press full charges.
If you have a healthy relationship with your boyfriend, the District Attorney is likely to take that into account. Be prepared to show the Commonwealth that you do have a healthy relationship. I would recommend that your boyfriend consult a criminal defense attorney to try to take some pre-emptive steps.
Honestly, you should talk to your parents and have them and a criminal defense attorney talk to the District Attorney.
Best of luck,
Shannon K. McDonald