OBJECTIVE: To compare the effect of delayed cord clamping on cord blood gas values in vaginally delivered, healthy, term singletons. DATA SOURCE: We used MEDLINE, CINAHL, CENTRAL, EMBASE, and databases. METHODS OF STUDY SELECTION: Eligible studies included randomized controlled trials (RCTs) comparing cord blood gas values obtained from early compared with delayed cord clamping groups and observational studies using serial cord blood gas from the same umbilical cord. We described the difference in means of cord blood gas parameters and comparative descriptive statistics when a difference in means was not available. We used a domain-based risk bias tool to extract methodologic details and assess potential risk of bias. TABULATION, INTEGRATION, AND RESULTS: This review included two RCTs and three observational studies. These studies included a total of 234 newborns with early cord clamping and 218 newborns with delayed cord clamping. The observational studies showed that 45-90 seconds delayed cord clamping was associated with mean decreases in umbilical arterial pH (0.02-0.03), HCO3 (0.3-0.8 mmol/L) and increases in base deficit (0.3-1.3 mmol/L) compared with early cord clamping. One observational study showed that delayed cord clamping was associated with decreases in umbilical venous pH (0.01) and HCO3 (0.2 mmol/L) and increase in venous base deficit (0.1-0.3 mmol/L) compared with early cord clamping. These changes were not observed in the two RCTs. CONCLUSION: Delayed cord clamping up to 120 seconds has either no effect or only a small effect on cord blood acid-base balance; overall, the magnitude of these changes is not clinically significant in vaginally delivered, healthy, term singletons. SYSTEMATIC REVIEW REGISTRATION: PROSPERO, CRD42019135779.
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