A policy of routine umbilical cord blood gas analysis decreased missing samples from high-risk births.
OBJECTIVE
This study compared obstetric units practicing routine or selective umbilical cord blood gas analysis, with respect to the risk of missing samples in high-risk deliveries and in infants with birth asphyxia.


METHODS
This was a Swedish population-based cohort study that used register data for 155 235 deliveries of live singleton infants between 2008 and 2014. Risk ratios and 95% confidence intervals were calculated to estimate the association between routine and selective umbilical cord blood gas sampling strategies and the risk of missing samples.


RESULTS
Selective sampling increased the risk ratios when routine sampling was used as the reference, with a value of 1.0, and these were significant in high-risk deliveries and birth asphyxia. The risk ratios for selective sampling were large-for-gestational age (9.07), preterm delivery at up to 36 weeks of gestation (8.24), small-for-gestational age (7.94), two or more foetal scalp blood samples (5.96), an Apgar score of less than seven at one minute (2.36), emergency Caesarean section (1.67) and instrumental vaginal delivery (1.24).


CONCLUSIONS
Compared with routine sampling, selective umbilical cord blood gas sampling significantly increased the risks of missing samples in high-risk deliveries and in infants with birth asphyxia.
Division of Clinical Epidemiology, Department of Medicine, Karolinska University Hospital, Stockholm, Sweden.|Division of Obstetrics and Gynecology, Department of Clinical Science and Education, Karolinska Institutet, South General Hospital, Stockholm, Sweden.
M
M
Ahlberg
Division of Clinical Epidemiology, Department of Medicine, Karolinska University Hospital, Stockholm, Sweden.
C
C
Elvander
Division of Clinical Epidemiology, Department of Medicine, Karolinska University Hospital, Stockholm, Sweden.
S
S
Johansson
Division of Clinical Epidemiology, Department of Medicine, Karolinska University Hospital, Stockholm, Sweden.
S
S
Cnattingius
Division of Clinical Epidemiology, Department of Medicine, Karolinska University Hospital, Stockholm, Sweden.|School of Public Health, University of California, Berkeley, CA, USA.
O
O
Stephansson
D001238:Asphyxia Neonatorum / Q000097:blood / Q000175:diagnosis*; D015415:Biomarkers / Q000097:blood; D001784:Blood Gas Analysis; D015331:Cohort Studies; D005312:Fetal Blood / Q000737:chemistry*; D006801:Humans; D007231:Infant, Newborn / Q000097:blood*; D016014:Linear Models; D015997:Neonatal Screening / Q000379:methods* / Q000592:standards; D010100:Oxygen / Q000097:blood*; D012042:Registries; D012306:Risk; D013548:Sweden
D015415:Biomarkers; D010100:Oxygen
Birth asphyxia; Cord blood gas analysis; High-risk deliveries; Population-based cohort