Congenital heart disease (a structural defect of the heart) affects 1% of newborns. Not all heart defects are serious, many close spontaneously or are so small that surgical repair offers little benefit. However, about 25% of congenital heart defects will require some kind of surgery or procedure in the first year of life. For many babies this surgery needs to happen soon after birth, so detecting these defects as soon as possible is critical.
Screening for CHD is difficult. All women who get prenatal care should have an ultrasound at 18-20 weeks, which should include a view of all 4 chambers of the heart. In reality, this ultrasound picks up 50% of heart defects at best. At 18-20 weeks the heart is maybe the size of an acorn. The blood vessels going to and from the heart are the size of spaghetti. The doctor is interpreting pictures taken of a moving target through both maternal and baby’s tissues. It is easy to see how things can be missed.
There is also a test called a fetal echo (a detailed ultrasound of the baby’s heart during pregnancy). Currently, a fetal echo is only performed if the initial ultrasound is abnormal or there is a much higher risk of heart defects (one example might be a mom who is taking lithium, a medication that increases the risk of certain heart defects). Echos are not a good screening tool. They are very expensive and there are only a limited number of technicians and doctors capable of performing and interpreting these scans. For the record, they are also not perfect. I had 2 fetal echos during pregnancy (as well as a very detailed 18 week ultrasound). All 3 scans missed BOTH of Oliver’s congenital heart defects, and my scans were performed at one of the top institutions for ultrasound in the U.S., if not the world.
Some have discussed the idea of doing an echo (heart ultrasound) on all babies at birth, but that is also expensive and not practical. An echo on a newborn requires specialized ultrasound technicians and pediatric cardiologists. There simply are not enough people available. These scans are also not infallible. Oliver had an echo at birth, it picked up his PDA, but missed his ASD and pulmonary stenosis. When his murmur persisted, another echo was performed and the 2 defects finally identified.
So that leaves us with two screening tools: a thorough physical exam and pulse oximetry (an indirect measurement of the amount of oxygen the blood is carrying).
Physical exam is hard because babies have an abnormal circulation for the first 24 hours. A heart murmur raises suspicion, but less than 15% of babies with a murmur are found to have significant CHD. In addition, doctors are not as good as examining the heart as they used to be, so many might miss the subtle findings on exam that should prompt further investigation.
For all these reasons, pulse oximetry after 24 hours of life is probably the best universal screening tool. Pulse oximetry measures how much oxygen the blood is carrying as a percent of its capacity. A cut-off value of 95% is used – below 95% and more tests are needed (95% means the blood is carrying 95% of the oxygen that it is capable of carrying). Pulse oximetry involves a probe on the foot or hand and is both painless and very inexpensive. Pulse oximetry adds an average of $1 to the hospital bill.
Pulse oximetry isn’t perfect, but it will pick up about 67% of babies with CHD. The other advantage of pulse oximetry is that the false positive rate is low. If 10,000 babies are screened, about 3-4 will test positive but on further testing be found to have no problem. So it won’t lead to too many babies getting unnecessary tests.
Pulse oximetry is inexpensive, readily available, and requires little training (a nurse used to testing adults should have some training before testing newborns). Women who wish to leave the hospital sooner than 24 hours after birth should realize that pulse oximetry screening for CHD cannot be performed before 24 hours. Women who are interested in CHD screening and plan on delivering at home should ask is their midwife has a pulse oximeter to bring to the house and if the midwife can make a visit between 24 and 48 hours to do the screening.
The data for this article comes form the joint statement of the American Heart Association and American Academy of Pediatrics on the role of pulse oximetry in newborns.
Remember, this blog does not represent individual medical advice.