Telling your boss?

Lindsay
Sorry in advance this is long!
I'm having a hard time deciding how to handle needing to take time off for dr. Appointments during work hours. I just had my first dr appointment on Tuesday @ about 8 weeks and took a half day vacation to accommodate (everything looked good so far! 😊😊)
My next ob appointment is 10/13 and it will be another 1/2 day event as the dr is about 30 min from my work, i have to get blood drawn, an ultrasound then the dr appointment.  Additionally I have my first genetic counseling appointment (hemophilia runs in my family)  Friday at 2 pm so another half day event.. I'm sure more will follow. 
Should I risk telling my boss too early to avoid using up vacation time for 1/2 days? Or  tell him and be able to say I have a dr appointment?