When pregnant do they have you pee in a cup to check for things like preeclampsia?

Yes: It is important to do this. In pregnancy many infections have no symptoms and can be easily detected in urine. Plus large amounts of proteins in urine can signal a possible preeclampsia.

Several basic issues: A urine screening gives the OB info on several basic risks in pregnancy. Puss or bacteria in the specimen suggests an infection which could create problems for mom & baby. Sugar in the urine would be a sign of emerging diabetes of pregnancy. Protein in more than minor amounts could be an early sign of the kidney damage in preeclampsia. A simple test with a lot of helpful info.