How does he tell his parents he got you pregnant when hes 18?

I would suggest telling one parent first and doing it at home. How to tell there is just to be straight forward and tell it like it is - "We messed up and this was not planned but now we are having a baby. I understand if you are angry and I'm sorry. I fully intend of being there as a dad and I hope you support us in this. I plan to get a job and finish school to be able to support my child."