Table 3

 Predictive values and likelihood ratios of historical variables for being not pregnant

Historic variableNegative HCGNPVLR-95% CI
*Likelihood ratio cannot be calculated as there were no positive results for subjects who stated they were not sexually active.
†There were no cases in which the patient stated that she “might be” pregnant but that there was “no chance” she could be pregnant.
CI, confidence interval; HCG, human chorionotropic gonadotropin; LMP, last menstrual period; LR-, negative likelihood ratio; NPV, negative predictive value.
Not sexually active (n = 130)130100.0%**
No to “chance pregnant” (n = 337)33699.7%0.130.02 to 0.82
No to “might you be”†(n = 444)43998.9%0.480.25 to 0.92
Uses birth control (n = 231)22896.1%0.470.18 to 1.25
LMP normal (n = 349)34396.0%0.740.43 to 1.27
LMP on time (n = 361)35694.9%0.590.38 to 1.13