The newest type of newborn screening in the United States is pulse oximetry screening for critical congenital heart disease. Sure, new diseases are added to the blood spot panel with some regularity. But CCHD screening is a whole different type of test, involving bedside or should we say, bassinet side diagnosis, using a point of care device known as a pulse oximeter. Wow, that's a lot of information. Let's get to the bottom of it. Congenital heart disease is actually a group of diseases. They are congenital, meaning that they're present at birth, but really the problem started much earlier, during the first trimester of pregnancy, during the period of organogenesis, when the organs were all just beginning to form. You see, congenital heart diseases are malformations or structural defects of the fetal heart. For one reason or another, the genetics dictating the process of the heart's formation were confused, causing defects. These defects in turn result in less than optimal functioning of the heart. Congenital heart disease is the most common kind of birth defect, with nearly one percent of all newborns being diagnosed with one. It is frequently stated that there are 18 different types of congenital heart diseases, but truly, there are variations on each type. Many of the lesions are not clinically significant, and others may resolve without intervention. Still others are significant enough that they interfere with normal growth and development of children. The severity of congenital heart disease varies according to the actual anatomy. For example, a ventricular septal defect or VSD can be a large or small hole and be located in the muscular or non-muscular portion of the septum, one of the important walls that separates the chambers of the heart. It can be the only problem, or it can be associated with other abnormalities. Critical congenital defects, however, are life-threatening. This group of congenital heart defects require surgical correction within the first month of life. About four out of every thousand babies born, will have a critical congenital heart lesion. It's super important to discover these before the baby leaves the birth center. Nowadays, cardiac surgery on newborns has developed to the point where all congenital heart lesions are considered to be operable. That means, they can be fixed surgically or at least modified to be functional. But if a baby goes home without having been diagnosed, over the course of a few days, they will become very sick. They may die or suffer severe symptoms, such as shock or acidosis, that can lead to long-term problems, and makes surgical correction even more difficult. Okay, so what if your patient had a prenatal ultrasound? Wouldn't that show a problem with the way the heart was formed? It's true the congenital heart disease is often picked up on prenatal ultrasound. But remember, the ultrasound is influenced by the equipment used, as well as the experience of the provider. In general, prenatal ultrasounds pick up about 50 percent of congenital heart lesions. Some lesions are notoriously difficult to diagnose prenatally. While you may ask if these defects are so serious, why would the baby had been discharged from the birth center? Wouldn't they have had symptoms? You would think so, but that's not always the case, it all has to do with the fact that the cardiovascular anatomy of the fetus is different from that of a baby after birth. Let's review the flow of blood in the baby and compare it to the fetus.