What are the three harmful things that can pass across placenta to fetus?

1. Infectious agents: These include bacteria, viruses, and parasites that can cause infections such as rubella, toxoplasmosis, and syphilis.

2. Toxic substances: These include alcohol, drugs, and certain medications that can cross the placenta and harm the fetus.

3. Maternal blood: If the mother has a condition such as preeclampsia, which causes high blood pressure and protein in the urine, it can lead to placental abruption, where the placenta separates from the uterine wall and the baby is deprived of oxygen and nutrients.