**Core Concept**
During pregnancy, the body undergoes various physiological changes to accommodate the growing fetus. One such change is the increased energy demand, which necessitates an increase in daily caloric intake. The first trimester is a critical period where the embryo's major organs and tissues begin to form.

**Why the Correct Answer is Right**
The daily extra calorie requirement in the first trimester of pregnancy is approximately 340 calories. This increase is primarily due to the energy demands of the growing embryo and the mother's increased metabolic rate. The additional calories are essential for the development and growth of the fetus, as well as for the mother's overall health and well-being. The energy requirements are estimated to be 10-15% more than the non-pregnant state.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not accurately reflect the estimated daily calorie requirement in the first trimester of pregnancy.
* **Option B:** This option is also incorrect as it is too high and does not align with the recommended daily calorie intake during the first trimester.
* **Option D:** This option is incorrect as it is too low and does not account for the increased energy demands of pregnancy.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the daily calorie requirements increase by approximately 340 calories during the first trimester, and by an additional 340-450 calories during the second and third trimesters. This increase in energy demands is crucial for the proper development and growth of the fetus.

**Correct Answer: C. 340 calories.**