early pregnancy loss early pregnancy loss early pregnancy loss is a medical term that when referring to humans can variously be used to mean: death of an embryo or fetus during the first trimester. this can happen by implantation failure, miscarriage, embryo resorption, early fetal resorption or vanishing twin syndrome. death of an embryo or fetus before 20 weeks gestation, as in all pregnancy loss before it becomes considered stillbirth.