Placenta
The baby in the womb gets everything it needs through the placenta.  Oxygen travels in the mother's blood from her lungs to the placenta and then in the baby's blood through the umbilical cord to the baby.  Carbon dioxide waste travels the same route in reverse, from the baby's blood to the mothers blood and out through her lungs.  Nutrient molecules (sugars, fats, proteins and vitamins) travel through her blood from her digestive tract to the placenta, and then in the baby's blood to the baby, and waste products travel back to her kidneys for disposal.