Patent Foramen Ovale in Fetal Development

Patent Foramen Ovale in Fetal Development

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An open foramen ovale after birth may cause circulatory problems.

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During fetal development, the formation of many organs begins early in pregnancy and continues until the time of birth. The fetal heart begins forming in the third week of pregnancy. As it develops, the heart partitions into 4 chambers. An opening called the foramen ovale develops between the upper chambers of the fetal heart. This opening is important for fetal circulation but normally closes shortly after birth.

Foramen Ovale

The fetal heart develops when 2 primitive tubes carrying fetal blood fuse into a single heart tube that undergoes complex folding, ultimately producing a 4-chambered heart. After birth, the 2 upper chambers -- the right and left atria -- receive blood from the baby's body and lungs, respectively. The two lower chambers -- the right and left ventricles -- pump blood to the infant's lungs and body, respectively. Because a developing fetus doesn't breathe or have functioning lungs, oxygen is delivered to the fetus from the mother through the placenta. Oxygen-rich blood travels from the placenta through vessels in the umbilical cord to the fetal right atrium. Since the fetal lungs are nonfunctional, the foramen ovale opening in the wall between the two atria allows fetal blood to bypass the lungs and flow directly into the left atrium. The foramen ovale has a thin flap that acts as a 1-way valve to prevent blood from moving in the opposite direction, from the left to right atrium.


When a baby is born and takes his first breath, significant changes occur in his circulation. The fetal vessels connecting to the placenta constrict and cut off the supply of placental blood to the fetal right ventricle. This lessens pressure on the foramen ovale and allows blood to flow directly from the right atrium into the right ventricle, which begins pumping blood to the infant's lungs. As the baby's circulation adjusts to the absence of the placenta and oxygenated blood begins to flow into the left atrium from the lungs, the pressure between the two atria equalizes. This cause the flap over the foramen ovale to remain in place, stopping blood from flowing between the atria. Over the next few months, the flap on the left side of the foramen fuses to the wall that divides the two atria, closing off the foramen ovale.

Prenatal Problems

Although problems with the function of the foramen ovale before birth are rare, any abnormality in its structure may interfere with fetal development and can cause serious problems. For example, if the foramen ovale is too narrow or totally closed, this prevents some or all of the oxygen-rich blood in the umbilical vessels from getting into the left ventricle and being circulated through the fetal body. This is a potentially serious problem that is sometimes associated with other malformations of the fetal heart. Depending on the severity of the heart problems, some fetuses with an abnormal foramen ovale may not survive.

Postnatal Problems

In about 1 in 4 adults, the foramen ovale remains partially to totally open. This condition is called a patent foramen ovale, or PFO. Most people with a PFO are symptom-free and unaware that they have the condition. However, having a PFO may play a role in causing migraine headaches, although why this might be so is not well understood. PFO may also raise the risk of having a stroke. An open foramen ovale could allow a blood clot to travel from the heart to the brain. In a review paper published in 2012 in the "Journal of the American College of Cardiology," the authors report that patients who have a stroke are significantly more likely to have PFO than people who have not had a stroke. The investigators also note that patients under age 55 who have a stroke of unknown origin are 6 times more likely to have a PFO, compared to people in the same age group who have not had a stroke. Therapy for a PFO can include medical treatment to reduce the likelihood of forming a clot, which may lower the risk of stroke but doesn't close the foramen ovale. Certain procedures may be effective in closing the foramen, including surgery to repair the opening or use of a closure device placed in the heart through a catheter in a vein or through the chest wall. If you have questions about PFO, talk with your doctor.