To determine whether hour of life and mode of delivery affect auditory brainstem response (ABR) results in healthy infants with a gestational age of >35 weeks.

This retrospective cohort study reviewed 31 984 infants tested during a standard birth hospitalization from 2014 to 2016 at Prentice Women's Hospital of Chicago. Per policy, ABRs were performed after 6 and 12 hours of life for vaginally and cesarean-delivered infants, respectively. Testing was repeated before discharge for infants who were referred once. For those infants who referred again, a third ABR was offered at no cost to families 10-14 days after discharge starting in 2016.

ABR pass rates consistently and significantly increased with advancing hour of life at testing, starting at 10-11 hours of life for vaginally born infants and 30-32 hours for cesarean-born infants. This steady, incremental increase in the pass rate was maintained overall until the vaginal and cesarean groups reached plateaus at 42-44 and 48-52 hours of life, respectively. In 2016 and beyond, a third hearing screen after discharge lowered the referral rate to just 0.77%.

This study of the results of ABR tests in over 30 000 well newborns demonstrates that delaying hearing screening until 10-11 hours for vaginally born infants and 30-32 hours for cesarean-born infants results in a statistically significant improvement in hearing pass rates.