In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan.


Spontaneous abortion or miscarriage is defined as the loss of pregnancy less than 20 weeks gestation. The American College of Obstetricians and Gynecologists (ACOG) estimates it is the most common form of pregnancy loss. It is estimated that as many as 26% of all pregnancies end in miscarriage and up to 10% of clinically recognized pregnancies. Moreover, 80% of early pregnancy loss occurs in the first trimester. The risk of miscarriage decreases after 12 weeks gestation.

The terms miscarriage and abortion are used interchangeably. The term abortion refers to a termination of a pregnancy either natural or induced. There are several terms that describe different states of pregnancy loss. These terms include threatened, inevitable, complete, and missed abortion. Threatened abortion is the presence of vaginal bleeding in early pregnancy but on pelvic exam, the cervical os is closed and the transvaginal ultrasound shows a viable fetus. Inevitable abortion is when there is vaginal bleeding but on the pelvic exam, the cervical os is open meaning that the fetus or products of conception are expected to pass through the cervix in the near future. On transvaginal ultrasound, there can be either be a viable fetus or not. Complete abortion is when there is initially vaginal bleeding and passing of products of conception through the cervix. On transvaginal ultrasound, there would be no remaining products of conception in the uterus. A missed abortion refers to when there was vaginal bleeding and perhaps some passage of tissue or products of conception. On pelvic exam, the cervical os would be closed. On transvaginal ultrasound, there would be retained products of conception and there would not be a viable fetus.

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