Pregnant and New Job

I just accepted a new job offer for pretty much my dream job. However, I have a high risk pregnancy since I’ve had several miscarriages before. I don’t really want to tell them about my pregnancy in case (heaven forbid) I have another miscarriage. Yet, the Dr wants me to come in every 2weeks for an ultrasound!

I haven’t even started the job yet, but would have at least 2 appointments during my first 30 days of employment which would require me to leave work 1.5 hours early. They said hours were flexible after training for 3 months, but obviously I’m not at that point yet. Help!