Does someone who has hidronephrosis can take pills to prevent pregnancy?

Yes: Yes but if you have reduced kidney function it is important to let your pcp or gynecologist know.

Yes: The hormones in the pill are metabolized in the liver so kidney issues are not a contraindication.

See below: Hydronephrosis may have left you with a reduced kidney function, which may affect your pregnancy. The doctor can help you understand the risks of taking contraceptive pills vs the hazards if any of a pregnancy with reduced kidney function. It all depends on the extent of loss of kidney function.