How does substances eaten or drunk by a pregnant woman end up in her baby's bloodstream?

Answer 1

If you imagine a baby to be a little like a parasite, this will help.

When a woman eats and drinks food, the essential nutrients, minerals and water are absorbed from it in the small and large intestine, where they are transferred into the bloodstream. When a woman becomes pregnant with a baby, one of the first things that will form in her womb is the placenta and the umbilical cord. These serve to absorb the nutrients the baby needs out of the woman's bloodstream, and into its blood.

Note here that this doesn't mean the baby shares the same blood - it has a different bloodstream altogether (that's why your baby can be a different blood type to you) and all it absorbs are the nutrients, and oxygen it needs, and excretes what it doesn't (waste like CO2) back into the mother's bloodstream through the placenta. (This process is called diffusion)

This is why it is so important not to smoke, drink alcohol, or take drugs when you are pregnant, as the baby will absorb all of those harmful toxins which affect its growth and in worst cases, result in the baby dying. Also, when the baby is born it can be addicted to the drugs you took while pregnant (including cigarettes) and then it goes through the same intense withdrawal symptoms you do as it is weaned off them in hospital. You can't take a baby home from hospital if it is addicted to anything. The nurses/doctors will keep it in and you will be reported to social services.