<prompt> Single best prognostic indicator of successful treatment with single-dose Methotrexate isGestational sac sizeSerum b-hCG levelAbsence of fetal cardiac activityPain abdomen  <response>: The best candidate for medical therapy is the woman who is asymptomatic, motivated, and compliant. With medical therapy, some classic predictors of success include a low initial serum b-hCG level, small ectopic pregnancy size, and absent fetal cardiac activity. Of these, initial serum b-hCG level is the single best prognostic indicator of successful treatment with single-dose MTX. Specifically, repoed failure rates are 1.5 percent if the initial serum b-hCG concentration is 1000 mIUmLReference: Williams Obstetrics; 25th edition; Chapter 19; Ectopic pregnancy 