my doctor told me when i was going to do it. you should call your doctor and ask. he or she should let you know when you'll have yours done!
I just did a walk in lab appointment.
I had to schedule it with the lab, but your doctor should've let you know !
I've always done it at my ob/midwives office. I'd give the office a call. They have always done it as a walk in lab appointment for me. Hope this helps.