**Core Concept**
During pregnancy, the body undergoes significant physiological changes to support fetal growth and development, increasing the demand for energy and nutrients. The daily caloric needs in pregnancy are higher than in the non-pregnant state to meet the increased metabolic demands of the mother and the growing fetus.

**Why the Correct Answer is Right**
The World Health Organization recommends an increase in daily caloric intake during pregnancy to support fetal growth and development. The recommended caloric increase is approximately 300 kilocalories per day in the first and third trimesters, with a higher increase in the second trimester. This increased caloric intake is essential to support the growth and development of the fetus, as well as to maintain the mother's overall health and well-being.

*Option A: 2000 kilocalories* is incorrect because it is the estimated daily caloric needs for a non-pregnant adult female, not pregnant women.
*Option B: 2500 kilocalories* is incorrect because it is the estimated daily caloric needs for a pregnant woman in the second trimester, but not the overall recommended increase.
*Option C: 3500 kilocalories* is incorrect because it is higher than the recommended caloric increase during pregnancy.

**Clinical Pearl / High-Yield Fact**
It is essential to note that the recommended caloric increase during pregnancy varies depending on the woman's pre-pregnancy weight and activity level. A well-balanced diet that includes plenty of fruits, vegetables, whole grains, and lean protein sources is crucial to support fetal growth and development.

**Correct Answer: B. 2500 kilocalories**