After Christine Malik gave birth to her first daughter three years ago, a clinician affiliated with a company called Pediatrix entered the hospital room and fitted the infant with sensors and wires for a hearing test. The child failed the screening required by law for all newborns, the tester said, requiring a follow-up exam. “We were scared as first-time parents,” said Malik, who agreed to the second exam. The clinician, Malik said, didn’t tell them that infants often fail an initial screening because of fluid from the womb in the ears that soon dissipates. The second screening found no problem with the baby’s hearing. Last year, when her second daughter was born, Malik refused a hearing test after another Pediatrix clinician appeared at her bedside. (Parents are allowed to opt out, but rarely do.) The infant hearing test—particularly the more advanced technology that Pediatrix uses—is an example of how some common medical …