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Life-saving test picks up baby heart defects

Pulse oximetry is usually done by clipping a small sensor onto a baby’s foot. Flickr/storyvillegirl

A quick, cheap and non-invasive test on newborn infants is effective in picking up heart defects missed by some prenatal ultrasounds, a UK study has found.

Pulse oximetry involves clipping a sensor to a finger or foot and measuring how light is absorbed. The degree to which red and infrared light is absorbed gives an indication of how well oxygenated the blood is. Poor levels of oxygenation in babies can indicate a heart defect such as a hole in the heart.

The test is commonly used on newborns in Australia where there is suspicion of a heart defect but authors of a new study published in the journal The Lancet suggest it should be done routinely, like hearing tests or a heel-prick test.

In a study on 20,055 newborns, the researchers found that pulse oximetry combined with prenatal screening and routine tests picked up 92% of critical congenital heart defects. Of the 53 cases of heart defects the test picked up, only 35 were already suspected after prenatal ultrasonography. At least 24 of the cases detected were critical, the paper said.

“Pulse oximetry is a safe, feasible test that adds value to existing screening. It identifies cases of critical congenital heart defects that go undetected with antenatal ultrasonography. The early detection of other diseases is an additional advantage,” the authors wrote in their paper.

Dr Dominic Wilkinson, Associate Professor of Neonatal Medicine and Bioethics at the University of Adelaide, pointed out that the experiment also delivered 169 false positives – cases where the pulse oximetry test suggested a problem but further investigation revealed there was none.

False positives can cause unnecessary anxiety, said Dr Wilkinson, who was not involved in the UK study.

“Every time you get a positive test, you then have to get the babies to have a formal cardio echo, which is much more involved, more expensive. You need an expert to do it and interpret the results and that may not be available in regional centres,” he said.

It was important to get the balance right between picking up serious defects and causing unnecessary alarm, he said.

“But overall, it looks to me like in this study that they have shown that the balance is pretty good. If they picked up 24 infants with critical heart disease while they were still in hospital, well that is a really important thing to do,” he said.

Dr Wilkinson also said the test may have greater use in places with lower quality ultrasound equipment, as most heart problems are picked up in a scan usually done when the mother is around 19 weeks pregnant.

“Another thing that is important is when babies are discharged from hospital. Certainly, in the UK they discharge babies earlier than they do here and most babies with congenital heart problems tend to run into trouble the first few days after birth,” he said. “If they are still in hospital when that happens, they are in a place when they can get medical attention.”

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