Thank you for reaching out to us. We are sorry to hear of your past miscarriages and appreciate the sensitive nature of this question.
Your first step is to speak with your physician as soon as possible to clarify:

If it is considered safe for you to start the fast
If so, what physical signs would indicate that the fast needs to be broken
If it could suffice to eat and drink in shiurim (small amounts).

See here for details about shiurim and for practical tips for fasting while pregnant.
Then please get back to us to follow up. For an immediate response, please call our telephone hotline or consult a local halachic authority.
Shana Tova and B’sha’a Tova!