Which of the following factors increases the risk of vitamin D deficiency in pregnant women?

Vitamin D deficiency is a significant concern during pregnancy, as adequate levels are essential for maternal and fetal health. Dark skin is associated with a higher risk of vitamin D deficiency primarily due to the increased melanin content, which acts as a natural sunscreen and reduces the skin's ability to produce vitamin D upon exposure to sunlight.

When pregnant women with darker skin are exposed to sunlight, their bodies synthesize vitamin D less efficiently than those with lighter skin. This can lead to a greater likelihood of having low vitamin D levels, especially if they live in areas with limited sun exposure or spend considerable time indoors. Thus, darker skin is a recognized risk factor for vitamin D deficiency in pregnant women due to these physiological and environmental interactions.

In contrast, factors like abundant sun exposure would generally decrease the risk of deficiency, while regular exercise and high-fat diets do not directly influence vitamin D synthesis in a meaningful way, further reinforcing the importance of skin pigmentation in this context.