## **Core Concept**
The double decidual sac sign (DDSS) is an ultrasound finding used to confirm an early intrauterine pregnancy. It is based on the appearance of the decidua parietalis and decidua capsularis surrounding the gestational sac.

## **Why the Correct Answer is Right**
The double decidual sac sign is characterized by two concentric hyperechogenic rings around the gestational sac. The **inner ring** represents the **decidua capsularis**, which is the layer of compact cells that covers the embryoblast (the part of the embryo that will form the fetus), while the **outer ring** represents the **decidua parietalis**, which lines the rest of the uterus. This sign helps in confirming that the pregnancy is intrauterine and not ectopic.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while it might relate to ultrasound findings or pregnancy, it does not specifically describe what the double decidual sac sign indicates.
- **Option B:** This option is incorrect for similar reasons; it does not accurately represent the significance of the double decidual sac sign.
- **Option D:** This option is incorrect because it does not correctly identify the indication of the double decidual sac sign.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that the double decidual sac sign is a critical ultrasound marker for confirming an early intrauterine pregnancy, helping to rule out ectopic pregnancy. Its presence is reassuring but not definitive; clinical correlation and follow-up ultrasounds are often necessary.

## **Correct Answer:** . Intrauterine pregnancy.