**Core Concept**
During pregnancy, the body undergoes significant changes to meet the increased metabolic demands of the fetus, placenta, and mother. The energy requirements of pregnancy are determined by the basal metabolic rate (BMR) plus an additional allowance to support fetal growth and maternal physiological changes.

**Why the Correct Answer is Right**
The energy needs of pregnancy are estimated to be 10-15% higher than the non-pregnant state. This increase is primarily due to the growth and development of the fetus, which requires a substantial amount of energy for protein synthesis, cell division, and tissue growth. Additionally, the mother's body needs to adapt to the increased metabolic demands of the fetus, including the production of new red blood cells and the expansion of maternal tissues.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not account for the increased energy needs of the fetus and the mother's physiological adaptations during pregnancy.
**Option B:** This option is incorrect because it underestimates the energy requirements of pregnancy, which are significantly higher than the non-pregnant state.
**Option C:** This option is incorrect because it is too high and does not reflect the average energy needs of pregnancy.

**Clinical Pearl / High-Yield Fact**
It is essential for healthcare providers to accurately estimate the energy needs of pregnant women to ensure adequate nutrition and prevent complications such as gestational diabetes and fetal growth restriction.

**Correct Answer: D. 10-15%**