Q&A: I am curious to know how long it takes for HCG hormone levels to decrease after a miscarriage or an abortion.

HCG, the hormone used to detect pregnancy, will decline slowly after a full-term pregnancy, sometimes taking as long as 12 weeks to go to 0 level. In a pregnancy that ends early, it will take a proportionately shorter period of time. Yes, there can be confusion if a subsequent pregnancy follows so closely that the hCG can't be distinguished between the last or the subsequent pregnancy. It makes us obstetricians confused, too. That is why it's good to get at least three good spontaneous menstrual cycles before attempting pregnancy again. And if pregnancy is not desired, for goodness' sake, use some contraception or abstinence.