A rapid decline in β-hCG concentrations over 2 days, commonly by 21-35% or more, is indicative of a spontaneous abortion or a resolving ectopic pregnancy. In an ectopic pregnancy, β-hCG concentrations are just as likely to fall as to rise, with no single pattern able to characterise the condition. However, 71% have serial serum β-hCG values that increase more slowly than would be expected with a viable IUP and decrease more slowly than would be expected with a spontaneous abortion.