my boss is my step father so he knew straight away as did my mum.
i told them because i wanted them to be aware if i had problems again.
last 2 times i told people about 8 weeks and then got bad news so this time i am definitely not telling work, people, friends or other family until the 12 weeks mark.
i think bosses are very understanding when you tell them your news and do what they can to make your job as easy as possible. well thats what i have found.