when is it the best time i should tell my boss im having a baby

Marie
I really dont know when it the best time to tell my boss im havving a baby .. im 7 weeks and feeling sleepy all the time .. which last week the doctors seen it in my eyes .. i work at a doctors office and when i found out i was .. my gyn said i should tell him bc i work with alot of sick people coming in and out of the office .. she even gave me a letter to give to my boss  but i havent done that yet .. plz i need advice .. i have my first sonogram on firday to see the baby and hear the baby heart beat