Perinatal determinants of the umbilical cord pH following preterm birth

Umbilical cord blood gas analysis captures the fetal acid-base balance at birth. We aimed to investigate the effect of antenatal and perinatal parameters on the cord blood pH and explore the association of cord pH with postnatal outcomes.

Retrospective cohort study of preterm infants born and admitted to the Neonatal Unit at King's College Hospital NHS Foundation Trust. The arterial and venous cord pH and the difference between the venous and the arterial pH were recorded (ΔpH).

From 2012 to 2023, 1,598 preterm infants (849 male) were included with a median (IQR) gestational age of 33.1 (30.4-35.1) weeks. The median (IQR) cord arterial pH was 7.27 (7.20-7.31) and cord venous pH was 7.32 (7.27-7.36). The arterial pH was significantly associated with the Apgar score at 10 min [unstandardised coefficient 0.021, 95 % CI: 0.015-0.027, adjusted p<0.001], the venous pH with the birth weight z-score [unstandardised coefficient 0.015, 95 % CI: 0.009 to 0.021, p<0.001] and the ΔpH with the administration of intrapartum antibiotics [unstandardised coefficient 0.015, 95 % CI: 0.006 to 0.025, p=0.002]. None of the indices were associated with the duration of invasive ventilation, the duration of stay or with survival to discharge from neonatal care.

Low arterial cord pH was associated with poor perinatal adaptation, low venous cord pH was associated with decreased fetal growth and a large difference between the two with possible perinatal infection.