Background: Umbilical artery blood gas (UABG) parameters serve as critical indicators of metabolic and oxygenation status in newborns at birth, including base excess (BE), pH, and lactate (LAC). In high-altitude hypoxic environments, the factors that influence these parameters in indigenous populations may be unique. This study aimed to identify the factors affecting UABG parameters among a low-risk, physiological Tibetan population at high altitude. Methods: This retrospective study analyzed data from 524 Tibetan women and their newborn babies who gave birth vaginally at a high-altitude hospital between January 1, 2024, and December 31, 2024. BE was the primary outcome, while pH and LAC were exploratory outcomes. Maternal and neonatal characteristics were categorized according to median pH, BE, and LAC values. Statistical methods, including t-tests, Mann-Whitney U tests, chi-squared tests, and linear regression models, were employed to identify factors influencing UABG. Results: The median (interquartile range IQR) values for UABG were pH: 7.28 (7.22, 7.33), BE: –8.00 (–10.00, –7.00) mmol/L, and LAC: 4.37 (3.47, 5.40) mmol/L. In univariate analyses, a lower pH (≤7.28) was associated with primiparity, shorter maternal height, longer second and third stage of labor, and neonatal length. A lower BE (≤–8.00 mmol/L) was associated with primiparity and longer first and second stages of labor. A lower LAC (≤4.37 mmol/L) was associated with multiparity, less frequent premature rupture of membranes, shorter second and third stages of labor, lower immediate blood loss, and total blood loss within 2 hours postpartum. Multivariable linear regression revealed maternal height as a positive predictor for pH (β = 0.002, p = 0.016), while the second stage duration was a negative predictor for pH (β = –0.001, p = 0.001) and BE (β = –0.017, p < 0.001), and a positive predictor for LAC (β = 0.003, p = 0.003). Neonatal length was a negative predictor for pH (β = –0.037, p = 0.005). Parity was a positive predictor for BE (β = 0.500, p = 0.045). Robust regression validated these associations. Significant differences were observed in pH, BE, and LAC between primiparous and multiparous women (p < 0.05). Significant differences were observed in BE between epidural anesthesia and non-anesthesia groups (p < 0.05). Conclusions: In this low-risk Tibetan population, pH was influenced by maternal height, the duration of the second stage of labor, and neonatal length. BE was influenced by parity and the duration of the second stage of labor. The duration of the second stage of labor is a factor influencing LAC. These results should not be generalized to high-risk pregnancies or complex delivery scenarios, as the study cohort was restricted to women with physiologically normal pregnancies who delivered vaginally.
Dongluo et al. (Thu,) studied this question.