**Core Concept**
In the context of early pregnancy, the presence of a gestational sac with a mean sac diameter (MSD) of 2-3 mm is a key indicator of viability. However, the presence of a yolk sac or embryonic pole is crucial for determining fetal viability.

**Why the Correct Answer is Right**
The calculation of the gestational age (GA) based on the crown-rump length (CRL) is a reliable method for assessing fetal development. In this case, the CRL of 5 mm corresponds to a GA of approximately 5.6 weeks. However, the presence of vaginal spotting and a well-formed gestational sac warrants further evaluation to confirm fetal viability. The next step would be to assess for the presence of a yolk sac or embryonic pole on transvaginal ultrasound (TVS) to confirm fetal development.

**Why Each Wrong Option is Incorrect**
**Option A:** Performing a beta hCG level would be premature at this stage, as the results would not provide additional information regarding fetal viability.
**Option B:** A repeat ultrasound in 7-10 days would be appropriate if there was no visible embryo or yolk sac, but not as the immediate next step.
**Option C:** A progesterone level would be useful in cases of suspected progesterone deficiency, but not in this scenario where the primary concern is fetal viability.

**Clinical Pearl / High-Yield Fact**
In early pregnancy, it is essential to recognize that a gestational sac with a CRL of 5 mm or greater typically indicates fetal viability. However, the presence of a yolk sac or embryonic pole is crucial for confirming fetal development.

**Correct Answer: D.**