Foetal acid-base status in clinical foetal distress and high risk cases

An investigation of the umbilical artery N-terminal proBrain natriuretic peptide levels of fetuses due to fetal distress in term pregnancies

OBJECTIVE

This study aimed to investigate umbilical artery N-terminal proBrain natriuretic peptide (NT-proBNP) in fetuses delivered by cesarean section due to fetal distress in term pregnancies.

METHODS

This prospective case-control study was conducted at the Antalya Training and Research Hospital Obstetric Department, Turkiye. A total of 140 pregnant women, 70 underwent elective cesarean sections between weeks 37 and 40 of gestation (Group 1, the control group) and 70 underwent cesarean sections due to fetal distress (Group 2, the study group), were included. The participants' sociodemographic and obstetric data and fetal umbilical blood NT-proBNP levels were recorded in a database.

RESULTS

Age, body mass index, gestational age, prenatal diagnostic tests, fetal anatomical scanning, and baby gender ratios were comparable between the groups (p>0.05), while statistically significant differences were observed in terms of gravidity (3.0 vs. 1.0, p≤0.001) and parity numbers (2 vs. 0, p≤0.001), baby height (50.36±0.88 vs. 49.80±0.86, p≤0.001) and weight (3422.43±409.16 vs. 3239.86±293.74, p=0.003), 1-min Apgar (9.0±0.1 vs. 8.5±1.3, p≤0.001) and 5-min Apgar (10.0±0.1 vs. 9.8±0.4, p=0.026) scores, umbilical artery pH (7.32±0.05 vs. 7.25±0.07, p≤0.001), umbilical artery base deficit (-2.48±1.23 vs. -4.36±1.09. p≤0.001), and NT-proBNP levels [8.77 (7.72-9.39) vs. 12.35 (9.69-12.92), p<0.001].

CONCLUSION

This study showed that NT-proBNP can be used as an important marker in the diagnosis of fetal distress. Prospective studies with more participants are now needed to confirm the accuracy of our results.

Maternal and fetal Acid-base chemistry: a major determinant of perinatal outcome

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.

Correlation between the foetal acid-base status and the Apgar score

The foetal pH values of eighty-eight cases delivered within 30 min after foetal blood sampling were correlated with the 1-min Apgar score. With a pH of 7·20 or above the error of prediction was 1·3%. The error in cases with pH below 7·20 was 54·5%.

Significantly higher pH and lower δ base deficit were present in the low foetal pH group in vigorous, as opposed to depressed infants, suggesting that infusion acidosis was present in infants with a high Apgar score.

The degree of correlation between the foetal pH and the Apgar score was not significantly influenced by shortening the sampling-delivery interval to 15 min or lengthening it to 3 hr. The most significant factor affecting the degree of correlation in the present study was the setting of the critical pH. If the criterion of the critical pH was taken as 7·13 there would have been no false positive results and the error of prediction in cases delivered within 30 min of foetal blood sampling would be reduced to 1·1%.