• Fetal loss at less than 20 weeks of gestation.
  NCI
  U.S. National Cancer Institute, 2021
• Spontaneous expulsion of a human fetus before it is viable.
  U.S. FDA Glossary
  U.S. Food & Drug Administration, 2021
• The natural premature expulsion from the uterus of the products of conception, the embryo, or non-viable fetus.
  CRISP Thesaurus
  National Institutes of Health, 2006
• (abortion, spontaneous) Expulsion of the product of FERTILIZATION before completing the term of GESTATION and without deliberate interference.
  NLM Medical Subject Headings
  U.S. National Library of Medicine, 2025
• Spontaneous abortion is noninduced embryonic or fetal death or passage of products of conception before 20 weeks gestation. Threatened abortion is vaginal bleeding without cervical dilation occurring during this time frame and indicating that spontaneous abortion may occur in a woman with a confirmed viable intrauterine pregnancy....
  Merck Manuals
  Merck & Co., Inc., 2025
• Miscarriage is the spontaneous loss of a pregnancy before the 20th week. About 10 to 20 percent of known pregnancies end in miscarriage. But the actual number is likely higher because many miscarriages occur so early in pregnancy that a woman doesn't realize she's pregnant.
  Mayo Clinic
  Mayo Foundation for Medical Education and Research, 2025
• Miscarriage is an involuntary, spontaneous loss of a pregnancy before 22 completed weeks. It is associated with unprovoked vaginal bleeding with or without suprapubic pain. The commonly used term, abortion, is unpopular with women who are uncomfortable with a suggestion that it follows an intentional attempt to terminate the pregnancy.
  Epocrates
  Athenahealth, Inc., 2019
• Miscarriage, spontaneous expulsion of the embryo or fetus from the uterus before the 20th week of pregnancy, prior to the conceptus having developed sufficiently to live without maternal support. An estimated 10 to 25 percent of recognized pregnancies are lost as a result of miscarriage, with the...
  Encyclopedia Britannica
  Encyclopedia Britannica, Inc., 2025