The cause of right hydronephrosis is that the increasing uterus often presses on the right ureter during pregnancy, which causes hydronephrosis in the right side of pregnant women. If the pressure of the uterus on the right ureter is more serious and there is obvious back pain or even urinary tract irritation signs such as frequent, urgent and painful urination, suggesting urinary system infection, it is best to go to the obstetrics department of the hospital in time for a systematic examination and treatment.