title: Detection of fetal heart activity in first trimester.
mesh_terms: D000033:Abortion, Threatened; D004452:Echocardiography; D005260:Female; D005318:Fetal Heart / Q000502:physiology*; D006801:Humans; D008722:Methods; D011247:Pregnancy; D011296:Prenatal Diagnosis; D013997:Time Factors; D014463:Ultrasonography