Nourishing food is a necessity both for a pregnant mother and a baby.

The word "nourishing" refers to food that provides essential nutrients and promotes health. In this context, the opposite of this would be "poor" (Option B) - to describe food that lacks nutritional value or is insufficient for maintaining health. The remaining options are a poor fit. For example, "unhygienic" (Option A) refers to cleanliness, not nutritional value. Similarly, "undercooked" (Option C) refers to the preparation of food, not its nutritional quality. Option D is also incorrect since "heavy" could refer to the feeling of fullness or perhaps even the density of food rather than its nutritional content.