Decidual Ring Thickness and Ultrasound Findings in Early Pregnancy

Understanding the Decidual Ring and Early Pregnancy Structures

The decidual ring represents the thickened endometrium surrounding the gestational sac in early pregnancy, and forms part of the "double decidual sac sign" or the "intradecidual sign," which can help identify intrauterine pregnancies, according to the American College of Radiology 1, 2
These signs have high specificity but poor sensitivity and interobserver agreement, making them helpful when present but not required for diagnosing an intrauterine pregnancy, as reported by the Radiology society 2

At 6-7 weeks gestation, more reliable prognostic indicators include the presence of a yolk sac, embryonic cardiac activity, and appropriate gestational sac growth, as indicated by the Radiology society 3, 4
Absence of expected structures based on gestational age or size may indicate poor prognosis, such as absence of yolk sac in a gestational sac >8 mm or absence of embryo in a gestational sac >16 mm, according to the American College of Radiology 5
Definitive diagnosis of nonviable pregnancy requires absence of embryo in a sac ≥25 mm or absence of cardiac activity in an embryo ≥7 mm, as stated by the American College of Radiology 5

When evaluating early pregnancy, the decidual ring thickness should be considered alongside other ultrasound findings rather than in isolation, as recommended by the American College of Radiology and Radiology society 1, 2
First trimester bleeding occurs in 7-27% of pregnancies, with overall miscarriage risk of approximately 12%, according to the American College of Radiology 6

Do not confuse decidual cysts with gestational sacs; decidual cysts typically lack an echogenic rim and are usually not adjacent to the central echogenic line of the collapsed endometrial cavity, as cautioned by the American College of Radiology 1
Avoid using terms like "pseudosac" or "pseudogestational sac" as they may lead to clinical errors; instead describe fluid in the endometrial cavity based on its characteristics, as advised by the Radiology society 3