**Core Concept**
Intrauterine fetal demise (IUFD) refers to the death of a fetus in the womb, typically occurring after 20 weeks of gestation. The diagnosis of IUFD often requires a combination of clinical evaluation, ultrasound findings, and laboratory tests.

**Why the Correct Answer is Right**
The correct answer is the "Double Decidua Sign". This sign is seen on ultrasound when there is a layer of decidua parietalis (the lining of the uterus) between the gestational sac and the uterine wall, which is a characteristic finding in IUFD. This occurs because the decidua parietalis grows over the uterine wall after fetal death, creating a double layer of decidua. This sign is often seen in conjunction with other ultrasound findings, such as the absence of fetal heart activity and the presence of fetal demise on Doppler ultrasound.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the diagnosis of IUFD.
**Option B:** While the "Gravida sign" may be seen in pregnancy, it is not a specific sign of IUFD.
**Option C:** This option is not a recognized sign of IUFD.

**Clinical Pearl / High-Yield Fact**
The Double Decidua Sign is a critical ultrasound finding in the diagnosis of IUFD. However, it is essential to note that IUFD can occur in any trimester, and the diagnosis should be made based on a combination of clinical evaluation, ultrasound findings, and laboratory tests, including fetal heart rate monitoring and maternal serum screening.

**Correct Answer: C. Double Decidua Sign**