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A fetus (baby) is fed, or nourished, by the mother through the placenta, which is attached to the umbilical cord. In the placenta, the mother's blood and the fetal blood both flow through vessels that are very close together. But the mother's blood does not mix with the fetal blood. When the mother's blood is close to the fetal blood, oxygen and nutrients move from the mother's blood into the fetal blood.
As the blood flows through the fetus, it picks up waste products and returns to the mother through the umbilical cord. The blood (with waste products from the fetus) goes through the mother's lungs and liver, where waste products are removed.
Since oxygen is supplied by the mother, the fetus does not use lungs to breathe. Only a small amount of blood flows to the fetus's lungs. After birth, blood must flow to the baby's lungs. Before birth, the mother's liver removes waste products for the fetus, so less blood flows through the fetus's liver.
Blood flows around the fetus's lungs and liver by going through an opening in the heart and through two extra blood vessels. This opening (called the foramen ovale) and the extra blood vessels (called the ductus arteriosus and the ductus venosus) normally close after birth.
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Last Revised: October 11, 2011
Author: Healthwise Staff
Medical Review: John Pope, MD - Pediatrics & Larry A. Latson, MD - Pediatric Cardiology
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