jules it is fantastic to have support from work when you are under going this. however, it isn't easy telling anyone especially those at work, so i understand where you are coming from, especially as you are new to the place. but, this is a life decision, a job is a part of the journey of life but a child is forever. i told my ex boss who was a father of three but seemed always complaining about his kids so i was worried he would ask why i would want to do this. turns out his SIL had done 5 IVF cycles so he was aware of the difficulties emotionally and physically and was really supportive of me. people are complex creatures and bosses should know from experience that we all have things going on in our lives and that flexibility and understanding in the workplace should actually mean you are happier and more productive in the workplace. i know i am. it is totally up to you, but sometimes you just don't know until you bring it up, and as sushee says the not knowing can be more stressful.

as to how to tell them, i don't know how your workplace works, but perhaps set up a time (in advance if possible) for a quiet, private conversation. that way they can see you are serious and you have their attention. you don't have to tell them the reasons why you have decided to do this, but a bit of the practicalities of how it may affect your work and how you plan to build it into your working day and how you see it working (provide them with some of the solution if they are worried about you not being there) could be a good way to go. it shows you are also serious and committed to your work but that you have a serious life issue also taking up your time emotionally and practically.

this is a medical issue, so they really don't have any right not to support you and they can not ask you to defer etc. you will have medical certs for procedures etc. most clinics have a stock of these for you to use.