Clots

I have passed two clots, the one the size of a dime & one that could fit on the tip of my finger. My baby is fine, and has a strong heartbeat. I rushed to the er both times to make sure everytjing was okay & they said everything was completely fine & normal. My HCG levels were also going up so I have no signs of miscarriage. I’ve also had no cramping along with the clots, and am only spotting brown which is only when i wipe. I have my first obgyn appointment in 4 days so thats when I will find out why I am passing clots, but has anyone else gone through this before? The doctors at the hospital said it could be because my body is trying to “get rid of old tissue”, but I would like to hear if anyone else has had a similar experience?