European completely confused by US insurance

I’m pregnant and now needing to use my health insurance for the first time (other than a few preventive things that were 100% covered). I’m so confused and stressed and hope somebody can explain it to me. If I go to an appointment, and they tell me I need x, y and z lab tests, how on Earth am I supposed to know if these will be covered and labs used in-network?I tried to ask my insurance provider (UHC) what is generally covered, and what tests are covered, but all they would say is that labs are generally covered 80% if in-network, but to check specific tests they need the procedure codes and lab names in advance. How do I logistically do this if even my doctor doesn’t know in advance which tests I will need? The only way I can see is if I refuse all tests, find out the codes and lab names, ask insurance if they’re covered, and go back for another appointment to get the labs taken. Or the admin staff call the insurance co during my appointment? How do people realistically handle this?