Objective Apgar scores of zero at 10 min strongly predict mortality and morbidity in infants. However, recent data reported improved outcomes among infants with Apgar scores of zero at 10 min. We aimed to review the mortality rate and neurodevelopmental outcomes of infants with Apgar scores of zero at 10 min in Japan.

Design Observational study.

Patients Twenty-eight of 768 infants registered in the Baby Cooling Registry of Japan between 2012 and 2016, at >34 weeks’ gestation, with Apgar scores of zero at 10 min who were treated with therapeutic hypothermia.

Interventions We investigated the time of first heartbeat detection in infants with favourable outcomes and who had neurodevelopmental impairments or died.

Main outcome measures Clinical characteristics, mortality rate and neurodevelopmental outcomes at 18–22 months of age were evaluated.

Results Nine (32%) of the 28 infants died before 18 months of age; 16 (57%) survived, but with severe disabilities and 3 (11%) survived without moderate-to-severe disabilities. At 20 min after birth, 14 of 27 infants (52%) did not have a first heartbeat, 13 of them died or had severe disabilities and one infant, who had the first heartbeat at 20 min, survived without disability.

Conclusion Our study adds to the recent evidence that neurodevelopmental outcomes among infants with Apgar scores of zero at 10 min may not be uniformly poor. However, in our study, all infants with their first heartbeat after 20 min of age died or had severe disabilities.