Maternal and fetal acid-base chemistry: A major determinant of perinatal outcome

Abstract

Very small changes in pH may significantly affect the function of various fetal organ systems, such as the central nervous system, and the cardiovascular system with associated fetal distress and poor Apgar score. Review of existing data on maternal-fetal acid-base balance in pregnancy highlight the factors that are associated with derangements of the acid-base status and the impact of the derangements on fetal outcome. Extensive search of electronic databases and manual search of journals for relevant literature on maternal and fetal acid chemistry, clinical studies and case studies were undertaken. There is a substantial reduction in the partial pressure of carbon dioxide (pCO2) in pregnancy. Adequate buffering prevents significant changes in maternal arterial pH. Normal fetal metabolism results in the production of acids which are buffered to maintain extracellular pH within a critical range. Fetal hypoxia can occur when maternal oxygenation is compromised, maternal perfusion of the placenta is reduced, or delivery of oxygenated blood from the placenta to the fetus is impeded. When adequate fetal oxygenation does not occur, metabolisms proceed along with an anaerobic pathway with production of organic acids, such as lactic acid. Accumulation of lactic acid can deplete the buffer system and result in metabolic acidosis with associated low fetal pH, fetal distress and poor Apgar score. There is a significant reduction in pCO2 in pregnancy. This change, however, does not result in a corresponding significant reduction in maternal arterial pH, because of adequate buffering. Very small changes in pH may cause significant derangement in fetal function and outcome.

Placental histology in clinically unexpected severe fetal acidemia at term

“…Several maternal and fetal diseases have been related to cord blood acidemia at birth [4] and maternal-fetal illness could also affect placental anatomy and function [5,6]: for example, maternal diabetes mellitus could impair acid-base balancing and could modify placental villous tree branching and angiogenesis.…”

Usefulness of clinical observations and blood chemistry values for predicting clinical outcomes in dairy goats with pregnancy toxaemia

“…It has been reported in sheep that very small changes in maternal pH may cause significant derangement is foetal function and outcome [12]. Since the percentage of the kids alive after caesarian surgery was lower (77 %) than those where parturition was induced (96 %) we hypothesised that the decreased rate of survival of the foetuses is also influenced by the lower blood pH.…”

Classification of caesarean section and normal vaginal deliveries using foetal heart rate signals and advanced machine learning algorithms

“…Figure 1 shows a scatter plot of the dataset with eclipses defining the separation between both case and control groups. Note that in this study 46 cases are classified as a caesarean delivery due to pH ≤7.20—acidosis, n = 18; pH >7.20 and pH ≤7.25—foetal deterioration, n = 4; or clinical decision without evidence of pathological outcome measures, n = 24 as defined in [14]. Table 1 provides details of the outcome measures used in the CTU-UHB database.

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