1. Nutrients: These provide the building blocks for the embryo's cells and tissues. They come from the mother's blood supply and are delivered through the placenta. These nutrients include carbohydrates, proteins, fats, vitamins, and minerals.

2. Oxygen: Embryos need oxygen to fuel their growth and development. Oxygen is also delivered through the placenta from the mother's blood.

3. Waste Removal: The embryo produces waste products as it grows. These waste products need to be removed from the body, and this is done through the placenta, where they are transferred to the mother's blood to be eliminated.

These three things are essential for a healthy embryo to develop into a healthy baby.