What is a harmful substance which could pass from the mother to the embryo?

One harmful substance that can pass from the mother to the embryo is alcohol. When a pregnant woman consumes alcohol, it can cross the placenta and affect the developing fetus, potentially leading to fetal alcohol spectrum disorders (FASDs). These disorders can cause a range of physical, behavioral, and cognitive impairments in the child. Other harmful substances include certain drugs, tobacco, and environmental toxins.