when to contact OB and maybe MFM?

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I'll have my second beta tomorrow. I've been here before and have even made it to 8weeks then had a loss, but I was constantly worried about the pregnancy from the beginning so I never even thought about this question. Anyway, when is it a good time to call the OB to let them know? I know I'll be under the care of my RE until 12 weeks. Do I just wait until I am released? Do I call them soon? And also, I'm thinking about possibly seeing a MFM with my RPL and the fact that I'm on Lovenox now. When would be a good time to find one?

TIA, sorry for all the crazy questions.