title: Population-based reference curve for umbilical cord arterial pH in infants born at 28 to 42 weeks.
abstract: The objective of the study was to examine normal variations of umbilical cord arterial pH by gestational age (GA).
  
  
  
  Population-based cohort study of 46 199 infants born from 2008 to 2014 in Stockholm, Sweden, with GA 28 to 42 weeks, Apgar score ⩾7 at 5 min, non-instrumental vaginal delivery, and birth weight for GA⩾3rd and ⩽97th percentile. Quantile regression was used to investigate the associations between GA and infant sex, and pH.
  
  
  
  The mean umbilical cord arterial pH (s.d.) was 7.29 (0.10), 7.27 (0.07), 7.25 (0.07) and 7.23 (0.07) among infants born at 28 to 31, 32 to 36, 37 to 41 and 42 weeks, respectively. Arterial pH decreased linearly with increasing GA, and female infants had higher pH than male infants (P<0.001).
  
  
  
  Umbilical cord arterial pH varied in a linear fashion by GA and was influenced by infant sex. The provided reference curve taking GA into account may yield a more accurate definition of acidosis at birth.
authors.affiliation: Department of Women's and Children's Health, Karolinska Institutet, Stockholm, Sweden.|Department of Neonatology, Karolinska University Hospital, Stockholm, Sweden.
authors.forename: B
authors.initials: B
authors.lastname: Skiöld
authors.affiliation: Department of Medicine Solna, Clinical Epidemiology Unit, Karolinska Institutet, Stockholm, Sweden.
authors.forename: G
authors.initials: G
authors.lastname: Petersson
authors.affiliation: Department of Medicine Solna, Clinical Epidemiology Unit, Karolinska Institutet, Stockholm, Sweden.
authors.forename: M
authors.initials: M
authors.lastname: Ahlberg
authors.affiliation: Department of Medicine Solna, Clinical Epidemiology Unit, Karolinska Institutet, Stockholm, Sweden.|School of Public Health, University of California, Berkeley, CA, USA.
authors.forename: O
authors.initials: O
authors.lastname: Stephansson
authors.affiliation: Department of Medicine Solna, Clinical Epidemiology Unit, Karolinska Institutet, Stockholm, Sweden.|Department of Clinical Science and Education, Karolinska Institutet, Stockholm, Sweden.
authors.forename: S
authors.initials: S
authors.lastname: Johansson
mesh_terms: D000138:Acidosis / Q000097:blood; D001724:Birth Weight; D015331:Cohort Studies; D005260:Female; D005312:Fetal Blood / Q000737:chemistry*; D005865:Gestational Age; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007231:Infant, Newborn; D007234:Infant, Premature / Q000097:blood*; D008297:Male; D012016:Reference Values; D012044:Regression Analysis; D012737:Sex Factors; D013548:Sweden; D014469:Umbilical Arteries