Went to the ER due to bleeding after intercourse and 4 weeks pregnant. My HGC level was 3700 then sent to my OB an hour later and they drew blood and my HGC level was 3573. Completed u/s and saw yolk sac and physical exam and felt my cervix was tightly closed and no signs of bleeding. Should I be concerned with the fact of my HCG level dropping or is that ol since it was within an hour of each other?

The levels can fluctuate depending on what test they use and how sensitive it is. If they're not concerned than you shouldn't be either. It sounds like everything is on track.

As CravenMorhead said, they will fluctuate. It is like any other hormone you have; they too will not remain the same level throughout the day. If the tests were done through different labs, that too can show a difference. Your difference in numbers is very slight. If you doctor was concerned, he would have scheduled you for another check in a few days time. You very well may have another ultrasound in a couple of weeks as a normal check.