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Blood flow through the heart changes after birth.
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While a fetus is the womb, the circulation of blood through the heart is different than it will be after delivery. Two circulatory openings present during fetal development close after delivery, the ductus arteriosus and foramen ovale. The alternate blood flow before birth is necessary because the fetal lungs are not yet functioning. Oxygen is supplied to the developing baby from the mother's bloodstream. The ductus arteriosus -- along with the foramen ovale -- allows the fetal blood to bypass the nonfunctioning lungs before birth.
Heart Anatomy and Oxygen
The heart consists of two upper chambers called the atria, and two lower chambers called the ventricles. After birth and throughout life, oxygen-poor blood from the body flows from the right atrium and ventricle to the lungs, where it picks up oxygen. From the lungs, the newly oxygenated blood travels to the left atrium and ventricle, where it is pumped to the body.
During pregnancy, fetal blood is oxygenated by the maternal circulation through the placenta and enters the fetus through the umbilical cord. Blood flows from the umbilical vein to the right atrium of the heart. From here, the fetal circulation differs because the ductus arteriosus and foramen ovale allow lung bypass routes for the already oxygenated blood entering the fetal right atrium.
Bypassing the Fetal Lungs
The foramen ovale is a valve-like opening that allows fetal blood to flow directly from the right atrium into the left atrium, bypassing the nonfunctioning fetal lungs. However, some fetal blood still passes from right atrium into the right ventricle. The ductus arteriosus is a second bypass mechanism that diverts fetal blood coming from the right ventricle away from the fetal lungs and into the main artery that distributes oxygen-rich blood to the developing baby's body.
Normal Circulation After Birth
When the lungs inflate and begin to function after birth, changes in pressure within the heart and circulation, and the release of several hormones and chemicals normally cause the ductus arteriosus and foramen ovale to close within hours to a few days after delivery. Closure of these fetal circulation bypasses allows blood to flow to the lungs to be oxygenated.
Problems After Delivery
In some babies, the ductus arteriosus does not close as it should after delivery. This condition -- known as a patent ductus arteriosus or PDA -- is a common congenital heart defect. PDAs occur more commonly in premature babies because their lungs are immature. A small PDA will often close on its own. If a PDA does not spontaneously close, medications, cardiac catheter techniques or surgery may be needed. Most full-term babies without other medical problems will live normal, healthy lives after their PDA is closed.