Adverse neonatal outcome and veno-arterial differences in umbilical cord blood pH (ΔpH) at birth: a population-based study of 108,629 newborns

BackgroundUmbilical cord blood gases are routinely used by midwives and obstetricians for quality assurance of birth management and in clinical research. They can form the basis for solving medicolegal issues in the identification of severe intrapartum hypoxia at birth. However, the scientific value of veno-arterial differences in cord blood pH, also known as Delta pH, is largely unknown. By tradition, the Apgar score is frequently used to predict perinatal morbidity and mortality, however significant inter-observer and regional variations decrease its reliability and there is a need to identify more accurate markers of perinatal asphyxia. The aim of our study was to investigate the association of small and large veno-arterial differences in umbilical cord pH, Delta pH, with adverse neonatal outcome.MethodsThis retrospective, population-based study collected obstetric and neonatal data from women giving birth in nine maternity units from Southern Sweden from 1995 to 2015. Data was extracted from the Perinatal South Revision Register, a quality regional health database. Newborns at >= 37 gestational weeks with a complete and validated set of umbilical cord blood samples from both cord artery and vein were included. Outcome measures included: Delta pH percentiles, 'Small Delta pH' (10th percentile), 'Large Delta pH' (90th percentile), Apgar score (0-6), need for continuous positive airway pressure (CPAP) and admission to neonatal intensive care unit (NICU). Relative risks (RR) were calculated with modified Poisson regression model.ResultsThe study population comprised of 108,629 newborns with complete and validated data. Mean and median Delta pH was 0.08 +/- 0.05. Analyses of RR showed that 'Large Delta pH' was associated with a decreased RR of adverse perinatal outcome with increasing UApH (at UApH >= 7.20: RR for low Apgar 0.29, P = 0.01; CPAP 0.55, P = 0.02; NICU admission 0.81, P = 0.01). 'Small Delta pH' was associated with an increased RR for low Apgar score and NICU admission only at higher UApH values (at UApH 7.15-7.199: RR for low Apgar 1.96, P = 0.01; at UApH >= 7.20: RR for low Apgar 1.65, P = 0.00, RR for NICU admission 1.13, P = 0.01).ConclusionLarge differences between cord venous and arterial pH (Delta pH) at birth were associated with a lower risk for perinatal morbidity including low 5-minute Apgar Score, the need for continuous positive airway pressure and NICU admission when UApH was above 7.15. Clinically, Delta pH may be a useful tool in the assessment of the newborn's metabolic condition at birth. Our findings may stem from the ability of the placenta to adequately replenish acid-base balance in fetal blood. 'Large Delta pH' may therefore be a marker of effective gas exchange in the placenta during birth.