Should I Tell My Parents?

Me and my fiance have been tryin 4 a baby 4 the last 4-5weeks bt have been talkin about it 4 the past 6months, i experienced pregnancy symptoms, so i did 2 tests both said NEGATIVE. I moved in wiv my fiance at the beginnin of May this year n frm then we set a date for when 2 start tryin. I want 2 tell my mum and dad about us tryin but i dont no wot 2 say n when would be the ryt tym 2 tell them, b4 or after? Meanin b4 we start tryin or when it happens? Does any1 have any tips or suggestions, i feel sooo 2 faced when we visit them, i jus want 2 tell them cos i dont want them 2 be disappointed in me! HELP!!