Subcategory	Definition	Ultrasound characteristics
Anembryonic gestation	Pregnancy in which a gestational sac develops without development of any embryonic structures; previously referred to as an “empty sac” or “blighted ovum”	Gestational sac > 13 mm without yolk sac or > 18 mm without embryonic pole, or empty sac beyond 38 days' gestation and no interval growth over one week
Complete abortion	All products of conception have passed	Empty uterus; endometrial lining may be thickened
Ectopic pregnancy	Any pregnancy outside of the endometrium; most commonly in the fallopian tube, but may also be in the cervix, cornua, ovary, or abdomen	Empty uterus; may see complex/cystic adnexal mass or fluid in cul-de-sac; embryo with cardiac activity is diagnostic but rarely seen
Embryonic or fetal demise	Pregnancy loss after the development of embryo or fetus; cervix closed and bleeding not present; also referred to as “missed abortion”	Embryonic pole ≥ 5 mm without fetal cardiac activity, or embryonic pole < 5 mm and no interval growth over one week
Incomplete abortion	Some, but not all, of the products of conception have passed	Heterogeneous and/or echogenic material along endometrial stripe or in cervical canal
Inevitable abortion	Cervix has dilated but passage of products has not occurred, and miscarriage is unavoidable; usually in setting of vaginal bleeding	Products of conception visible; fetal cardiac activity may or may not be present
Recurrent abortion	Three or more consecutive pregnancy losses	—
Septic abortion	Incomplete abortion associated with ascending infection of the endometrium, parametrium, adnexa uteri, or peritoneum	Findings consistent with incomplete abortion
Threatened abortion	Bleeding before 20 weeks' gestation with closed cervix; pregnancy viable at time of presentation and may or may not miscarry	Findings appropriate for stage of pregnancy; subchorionic hemorrhage may be present