Patent Foramen Ovale: A Common Heart Anomaly in Pregnant Women

In previous articles on The Pulse, we have covered the rare but serious complication of strokes occurring during pregnancy, resulting from increased tendency to form blood clots, and we have also touched on the topic of congenital conditions leaving a hole between the two atria (upper chambers) of a baby’s heart. Hearing about such congenital heart malformations, you may think of young children automatically. After all, congenital conditions are the main issue that concern us when it comes to newborns, as they are born and develop into young children. But today, let’s explore what happens when the baby with the most common type of structural heart issue, a type of hole known as a patent foramen ovale (PFO) grows up and sets out to have children of her own. We are choosing to focus on PFO as today’s example, because it is extremely common. It occurs in an estimated 25 to 30 percent of people; that’s so common that we cannot even refer to PFO as a disease.

Before considering PFO in the context of pregnancy, let’s take a look at how to classify PFO in relation to what is normal and what is not. A hole between the two atria of the heart can be either an atrial septal defect (ASD), meaning that a portion of the the atrial septum (the wall between the two atria) is simply missing. This can happen in an adult either from a very bad heart attack that damages the septum, which is extremely rare in a woman of childbearing age, or, in almost all cases, as a result of the interatrial septum never completing its formation in the first place, that is during fetal life. Much, much more common, however is a PFO, which is different from an ASD the way that a broken door is different from a hole in the wall of your house. During fetal life, right up to birth, a part of the interatrial septum has a kind of swinging door, on an opening through the septum, called the foramen ovale. Have you ever seen an old western movie in which some guy walks into a saloon, busting through swinging doors, that move back and forth in both directions? Well, that’s not the type of swinging door that you have in your heart. Think instead about the kind of swinging door that can swing only one way, either into or out of a room. In the heart, between the right and left atria, the door through the foramen ovale swings in the direction toward the left atrium. Consequently, when you were a fetus and your lungs were all collapsed and full of fluid, keeping the pressure in the lungs high, the pressure in your right atrium was high, higher than the pressure in your left atrium. This kept the foramen ovale open, allowing blood to move freely from the right side of the heart to the left. When you were born however, and took your first breaths of air, the lungs inflated, the pressure in the right atrium decreased dramatically, while the pressure in the left atrium increased, leading to the post-birth circulatory situation, characterized by a high pressure on the left side of the heart and a low pressure on the right side.

Now, in most people, over the course of weeks to months, the swinging door of the foramen ovale, not only stays shut because of the higher pressure in the left atrium pushing it shut, but also because locks shut. Actual physical connections form, making it more like a locked door than like a swinging door. But in those 25-30 percent of people, the door never locks, which means that it could swing open on some occasions —namely, when the pressure in the right atrium increases significantly compared with the pressure in the left atrium. When might such a pressure change occur in a pregnant woman?

First of all, it happens whenever the volume of blood entering the right atrium increases, and that happens during pregnancy. As pregnancy progresses, the volume of blood in a woman increases typically about 50 percent and in some women the increases can even approach 100 percent. Increased right atrial pressure also could happen during scuba diving — which is not something that you are not supposed to do while you are pregnant— but there is something that everybody does, whether pregnant or not. It’s called a Valsalva maneuver, a sudden increase of pressure in your thorax against a closed glottis. This happens when you cough, laugh, or strain to go to the potty number two and also in certain very high stress situations, when you need to raise the pressure in your abdomen and thorax and keep it high for moments at a time, such as when you lift something very heavy (which you shouldn’t do while pregnant), or when prevent yourself from losing consciousness while flying a high performance aircraft through a high acceleration maneuver (which also is not recommended during pregnancy).

Or, when you push during vaginal delivery, to get the baby out. This is the situation that worries people and may lead your obstetrician to recommend cesarean birth, but the good news is that, despite the very high prevalence of PFO among healthy adults, many PFOs produce only very mild changes in the types of things that could cause a problem. Consequently, the simple presence of a PFO, as opposed to certain more serious cardiac anomalies that we’ll discuss in future posts, may not put you at serious risk, nor necessitate that you have a C-section, although the option would be open to you.

So what types of changes and problems are we concerned might result from an increased pressure in the right atrium pushing open the swing door? The main issue is that it could lead to a stroke, due to blood from the right atrium moving directly into the left atrium, thus bypassing the lungs. Such a stroke would be initiated by an embolus reaching the brain and causing an embolism, after breaking off from another clot, either in a deep vein, or in the heart itself. The first scenario, an embolus coming from a clot in a deep vein, is something that we have discussed previously on The Pulse, and for which pregnant women are at particular risk. The second scenario, an embolus from the heart itself, can result from what doctors call an atrial septal aneurysm, which can occur in association with a PFO, or more likely with an ASD.

The presence of any of these structural heart conditions —PFO, ASD, atrial septal aneurysm— can be determined with a technique called cardiac ultrasonography, which works on your heart just like the ultrasonography that is used on your uterus to examine your fetus. While most PFOs are very mild and do not require treatment during pregnancy, more severe cases can be treated using instruments that are passed through blood vessels to close the opening in the atrial septum without surgery.

David Warmflash
Dr. David Warmflash is a science communicator and physician with a research background in astrobiology and space medicine. He has completed research fellowships at NASA Johnson Space Center, the University of Pennsylvania, and Brandeis University. Since 2002, he has been collaborating with The Planetary Society on experiments helping us to understand the effects of deep space radiation on life forms, and since 2011 has worked nearly full time in medical writing and science journalism. His focus area includes the emergence of new biotechnologies and their impact on biomedicine, public health, and society.

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