Serum progesterone (P) levels were determined at the time of routine prenatal registration (227 patients) or upon presentation for evaluation of vaginal bleeding and/or abdominopelvic cramping/pain (135 patients). P associated with a normal intrauterine gestation was 24.63 +/- 4.19 (SD) ng/mL as compared with 6.29 +/- 2.43 ng/mL and 6.02 +/- 2.39 ng/mL for spontaneous abortions and ectopic gestations, respectively. Further, P differed between asymptomatic (11.92 +/- 9.61 ng/mL) and symptomatic patients (4.81 +/- 3.92 ng/mL) who were subsequently shown to have an abnormal gestation. By establishing a P cutoff point of < or = 14.2 ng/mL and