<prompt> All the following are criteria to diagnose postmolar GTN exceptPlateau of serum b-hCG level - 10 percent for four measurements during a period of 3 weeks or longerRise of serum b-hCG level 10 percent during three weekly consecutive measurements or longer, during a period of 2 weeks or moreSerum b-hCG level remains detectable for 2 months or moreHistological criteria for choriocarcinoma  <response>: Criteria for Diagnosis of Gestational Trophoblastic NeoplasiaPlateau of serum b-hCG level - 10 percent for four measurements during a period of 3 weeks or longer Rise of serum b-hCG level 10 percent during three weekly consecutive measurements or longer, during a period of 2 weeks or more Serum b-hCG level remains detectable for 6 months or more Histological criteria for choriocarcinomaReference: Williams Obstetrics; 25th edition, chapter 20; Gestational trophoblastic diseases 