(845) Adverse perinatal outcome and veno-arterial differences in umbilical cord pH at birth: a population-based study

Analysis of cord blood gases, especially cord arterial pH (UApH), can identify newborns at risk of adverse outcomes, yet the scientific value of veno-arterial differences in cord pH (ΔpH) is largely unknown. By tradition, the Apgar score is frequently used to predict perinatal morbidity and mortality, however, significant inter-observer variations decrease its reliability and there is a need for more accurate markers of perinatal asphyxia. The objective of our study was to investigate the association of ΔpH to risk for adverse perinatal outcome.


Study Design:

This retrospective, population-based study collected obstetric and neonatal data from women giving birth in nine Swedish maternity units from 1995-2015. Newborns at ≥37 gestational weeks with a validated set of umbilical cord blood samples were included. Outcome measures included: ΔpH distribution, small ΔpH (10^th percentile), large ΔpH (90^th percentile), Apgar score (0-6), need for continuous positive airway pressure (CPAP) and neonatal intensive care unit (NICU). Relative risks (RR) were calculated with modified Poisson regression.


Results:

The final study population comprised of 108 629 newborns with validated data. Mean and median ΔpH was 0.08 ± 0.05. Analyses of RR showed that large ΔpH 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 ΔpH was associated with an increased RR for low Apgar score and NICU admission only at higher UApH values (at UApH ≥7.20: RR for low Apgar 1.65, P=0.00, RR for NICU admission 1.13, P=0.01).


Conclusion:

Large ΔpH was associated with a decreased risk for adverse perinatal outcome including low Apgar score, need for CPAP and NICU admission. Clinically, ΔpH 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 leading to a large ΔpH. A large ΔpH may therefore be a marker of effective gas exchange in the placenta during birth.