**Core Concept**
The **Spalding sign** is a radiological feature observed in fetal death, characterized by overlapping of the bones of the skull. This sign is crucial in the diagnosis of intrauterine death, especially in patients with systemic lupus erythematosus (SLE) who are at higher risk of pregnancy complications.

**Why the Correct Answer is Right**
The correct answer is related to the timeframe when the Spalding sign becomes visible on an ultrasound scan after fetal demise. The sign typically appears as the fetus's soft tissues undergo maceration and the bones of the skull start to overlap due to the loss of tissue integrity.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Spalding sign does not appear immediately after fetal death.
**Option B:** This choice is also incorrect as it does not accurately reflect the earliest time frame for the appearance of the Spalding sign.
**Option D:** Similarly, this option is incorrect as it suggests a later appearance of the sign than what is typically observed.

**Clinical Pearl / High-Yield Fact**
In patients with SLE, it is essential to monitor fetal movement and perform regular ultrasound scans to detect any signs of fetal distress or demise promptly. The Spalding sign is a critical marker of intrauterine death and should be recognized early to guide further management.

**Correct Answer:** D. 7 days