Threatened Miscarriage

I went to the ER three weeks ago with bleeding, and was diagnosed with a threatened miscarriage. I was told to follow up with my OB within the week. However, when I did the nurse told me that there was nothing else they could do, and that if I saw a heartbeat at the ER, that was the best thing I could see. I asked her if there was any sort of blood work we could do to help determine the cause or possible methods of treatment. She said “No, not really.” But she seemed unsure. I didn’t want to antagonize her, so I decided to trust her professional opinion— figuring I was just being paranoid because of my previous miscarriage. I found out earlier this week that the baby has died. I can’t help but feel there’s more they could have done— like check my progesterone—but I’m not a doctor. Is there anything an OB should do, at a minimum, when someone is having a threatened miscarriage? Or is it normal to have them take such a passive approach to it?