The problem arises if hearing screening tests are done within a baby's first two days of life, researchers say. At that point, newborns delivered by C-section have a higher failure rate than babies born by vaginal delivery.

So to avoid needless repeat tests -- and anxiety for parents -- the researchers are recommending a delay in hearing tests for C-section babies.

The American Academy of Pediatrics recommends that all infants have their hearing tested before they are one month old. That's often done before a newborn leaves the hospital, though it varies by country and hospital.

The new study looked at more than 1,600 infants born at one Israeli hospital, where all newborns have their hearing evaluated before going home.

Researchers found that when babies born by C-section had their hearing tested in their first two days of life, about 21 percent failed the test. That compared with seven percent of babies delivered vaginally -- a three-fold difference.

The gap narrowed when the researchers looked at babies tested after two days: eight percent of C-section babies failed, versus one percent of vaginally delivered babies.

And in the end, all of the babies referred for further hearing tests passed, meaning that the failures had all been false alarms.

After a C-section, new parents "should be aware of the...temporary failure on hearing screening, and can ask for a delayed screening beyond 48 hours of age," Dr. Tatiana Smolkin and Dr. Imad R. Makhoul, the study leaders, said in an email.

Babies born by C-section typically stay in the hospital longer because their moms need a longer recovery. At their hospital, Smolkin and Makhoul said, those newborns will typically stay four to five days.

So delaying a first hearing test should not be a practical problem.

The researchers, who are based at Meyer Children's Hospital in Haifa, report the findings in the journal Pediatrics.

It's not clear from the study why C-section newborns tend to fare worse on very early hearing tests.

But Smolkin and Makhoul said it is likely related to fluids in the middle ear. Normally, a baby's journey through the birth canal pushes those fluids out. A baby born by C-section bypasses all of that -- and the middle-ear fluids are retained for a couple days.

In the U.S., universal newborn hearing screening was first recommended in the 1990s. Now nearly all infants are screened, according to government statistics. But the timing varies. Studies have found that anywhere between 40 percent and 92 percent of newborns are screened before leaving the hospital, depending on the center, Smolkin and Makhoul said.

The cost of screening in the U.S. has been estimated to fall between $10 and $50 per infant. If C-section babies' first tests were put off a bit, that could help cut costs by preventing unnecessary repeat tests, according to Smolkin and Makhoul.

And, they said, it could save more parents needless worry.

SOURCE: bit.ly/KqCEzf Pediatrics, online June 11, 2012.

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