**Core Concept**
The diagnosis of pregnancy involves several methods, each with varying degrees of reliability and accuracy. While certain signs and symptoms are indicative of pregnancy, a definite diagnosis can be made through more objective and direct means.

**Why the Correct Answer is Right**
Human chorionic gonadotropin (hCG) in blood is a sensitive marker for pregnancy, but it can also be present in non-pregnant individuals, particularly those with certain types of tumors or conditions. Therefore, a positive hCG test in isolation is not sufficient to confirm pregnancy definitively. In contrast, other methods listed involve more direct visualization or palpation of fetal structures, which provide stronger evidence of pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** Fetal heart sound can be detected through auscultation as early as 10-12 weeks of gestation, indicating a viable intrauterine pregnancy. This method is more reliable than hCG levels alone.
**Option B:** Palpation of fetal parts, such as the uterus or fetal movements, is a more direct and reliable indicator of pregnancy than hCG in blood. This method has been used for centuries to confirm pregnancy.
**Option C:** Fetal skeleton on X-ray can be visualized as early as 14-16 weeks of gestation, providing strong evidence of intrauterine pregnancy. This method is more accurate than hCG levels alone.

**Clinical Pearl / High-Yield Fact**
In forensic medicine, the presence of fetal heart sounds or palpable fetal parts is considered strong evidence of pregnancy, whereas a positive hCG test may be inconclusive due to the potential for false positives.

**Correct Answer:**
✓ Correct Answer: D. hCG in blood