New Findings on Umbilical Cord pH Levels Highlight Need for Updated Thresholds in Neonatal Care

In the cohort study involving 340,431 newborns, the findings confirm and expand on previous research, showing that adverse outcomes can occur even when umbilical cord pH levels are above 7.00. This suggests that it may be necessary to re-evaluate the current threshold for more intensive monitoring and treatment.

These findings suggest that the threshold for more intensive observation and treatment in cases of acidosis may need to be re-evaluated, the researchers wrote in JAMA Network Open. 

Umbilical cord pH (UC-pH) is a crucial objective marker for detecting intrapartum fetal hypoxia and predicting neonatal morbidity and mortality. While a UC-pH value below 7.00 is typically used to indicate severe acidosis, existing evidence varies and is primarily derived from UC-pH measurements in selected populations, making the results difficult to interpret. Charlotte Brix Andersson, Department of Obstetrics and Gynaecology, Aalborg University Hospital, Thisted, Denmark, and colleagues aimed to investigate the association between UC-pH levels and adverse neonatal outcomes risk in a national setting with universal UC-pH measurement.

This national, population-based cohort study examined liveborn, singleton, full-term infants without malformations born in Denmark between January 1, 2012, and December 31, 2018. Data were analyzed from January 1, 2023, to March 1, 2024.

Umbilical cord pH levels were categorized into four groups: less than 7.00, 7.00 to 7.09, 7.10 to 7.19, and 7.20 to 7.50 (the reference group).

The primary outcome was a composite measure of severe adverse neonatal outcomes, including neonatal death, therapeutic hypothermia, mechanical ventilation, treatment with inhaled nitric oxide, and seizures. Secondary outcomes included the individual components of the primary outcome, as well as Apgar scores, respiratory outcomes, and hypoglycemia.

The study led to the following findings:

• Among the 340 431 infants included, the mean gestational age was 39.9 weeks; mean birth weight was 3561 g, and 51.3% were male.
• Umbilical cord pH of less than 7.20 was observed more often among infants with a gestational age of 40 or 41 weeks (31.6%-33.6% compared with 18.2%-20.2% at a gestational age of 39 weeks) and among male infants (53.9%-55.4% versus 44.6%-46.1% among female infants).
• Compared with the pH reference group (0.2%), there was an increase in the risk for the primary outcome for the groups with UC-pH levels of less than 7.00 (9.8%), 7.00 to 7.09 (0.8%), and 7.10 to 7.19 (0.4%).
• Comparable patterns were observed for the individual outcomes, except for neonatal death, which was only increased in the group with UC-pH levels of less than 7.10.
• The risk of treatment with continuous positive airway pressure increased when UC-pH levels were less than 7.20, and the risk of hypoglycemia was 21.5% if UC-pH levels were less than 7.10.

"Understanding the risk of neonatal adverse outcomes at varying umbilical cord pH levels may prompt a re-evaluation of the thresholds for more intensive monitoring to identify conditions that warrant intervention. Future research should focus on assessing the long-term risk of adverse outcomes extending into childhood," the researchers concluded.

Reference:

Andersson CB, Klingenberg C, Thellesen L, Johnsen SP, Kesmodel US, Petersen JP. Umbilical Cord pH Levels and Neonatal Morbidity and Mortality. JAMA Netw Open. 2024;7(8):e2427604. doi:10.1001/jamanetworkopen.2024.27604