1 Hospital General Universitario Gregorio Marañón, Instituto de Investigación Sanitaria, Pediatric Intensive Care Unit, Madrid, Spain; Maternal and Child Health and Development Network, RETICS funded by the PN I+D+I 2013-2016 (Spain), ISCIII-Sub-Directorate General for Research Assessment and Promotion and the European Regional Development Fund (ERDF), Madrid, Spain.
2 Hospital General Universitario Gregorio Marañón, Instituto de Investigación Sanitaria, Pediatric Intensive Care Unit, Madrid, Spain; Maternal and Child Health and Development Network, RETICS funded by the PN I+D+I 2013-2016 (Spain), ISCIII-Sub-Directorate General for Research Assessment and Promotion and the European Regional Development Fund (ERDF), Madrid, Spain; Universidad Complutense de Madrid, Facultad de Medicina, Departamento de Salud Pública y Maternoinfantil, Madrid, Spain. Electronic address: pielvi@hotmail.com.