The beneficial effect of prophylactic hydrocortisone treatment in extremely preterm infants improves upon adjustment of the baseline characteristics.

"Competing interests The authors thank Aguettant Pharma for a provided unconditional grant. This financial sponsor had no implication in study design, data collection, analysis, decision to publish or preparation of the manuscript."

"Funding information This work was supported by a research grant from the French Ministry of Health and sponsored by the Département de la Recherche Clinique et du Développement, Assistance Publique-Hôpitaux de Paris (AOM 06 025 and AOM 11 129). The authors thank Aguettant Pharma for a provided unconditional grant. This financial sponsor had no implication in study design, data collection, analysis, decision to publish, or preparation of the manuscript. Open access funding provided by University of Geneva."

"Registration numbers EudraCT number 2007-002041-20, ClinicalTrial.gov number NCT00623740."