## Core Concept
The first trimester of pregnancy is a critical period where various physiological changes occur. Obstetrical signs during this period help in confirming and assessing the pregnancy. These signs can be related to the uterus, cervix, or other associated changes.

## Why the Correct Answer is Right
The correct answer, . (Chadwick's sign), is a recognized early sign of pregnancy. It refers to the bluish discoloration of the cervix, vagina, and vulva due to increased blood flow. This is a true sign associated with early pregnancy.

## Why Each Wrong Option is Incorrect
- **Option A:** (Hegar's sign) is a true sign. It is characterized by the softening of the lower part of the uterus (isthmus) just above the cervix, which can be felt during a bimanual examination.
- **Option B:** (Goodell's sign) is also a true sign. It refers to the softening of the cervix, which occurs early in pregnancy.
- **Option D:** (Prague's sign) or (also known as the "Prague sign" or "Kernig's sign" in some contexts) might not directly correspond to a widely recognized first-trimester sign by this name; however, there are several signs in obstetrics, and misidentification or confusion can occur.

## Clinical Pearl / High-Yield Fact
A key point to remember is that while several signs are indicative of early pregnancy, such as Hegar's, Goodell's, and Chadwick's signs, they are most accurately assessed through a combination of clinical examination and ultrasound confirmation.

## Correct Answer: D.