Accuracy of intrapartum fetal blood gas analysis by scalp sampling

Abstract

Fetal blood gas analysis (FBGA) using scalp blood is commonly used to identify serious fetal distress. However, there is a lack of data regarding its accuracy and reliability. The aim of this study was to determine the positive predictive value (PPV) and negative predictive value (NPV) of FBGA for predicting postpartum acidosis in case of nonreassuring fetal heart rate tracings (NRFHRT). To this end, we conducted a retrospective cohort study of singleton term deliveries with NRFHRT according to Fédération Internationale de Gynécologie et d’Obstétrique and Fisher cardiotocography scores undergoing FBGA in a university hospital. The PPV and NPV of FBGA regarding neonatal acidosis (defined as a pH value ≤ 7.15 in arterial or venous umbilical cord blood) and Apgar scores indicating neonatal depression (defined as a 5-min Apgar score ≤5) were evaluated. Multivariate analysis was used to determine the influence of cardiotocography variations and the time delay between FBGA and delivery on the accuracy of FBGA. We analyzed 343 deliveries with NRFHRT. In 32 (9%) of these cases, fetal acidosis was confirmed by a postpartum umbilical cord blood pH value ≤ 7.15. In 308/343 (90%) cases, FBGA identified NRFHRT as false positive (as confirmed by nonacidotic postpartum pH values) and thus avoided unnecessary interventions such as operative delivery. The overall test accuracy of FBGA was 91%. FBGA accurately predicted postpartum cord blood pH values with a margin of ±0.2 in 319/343 (93%) cases. On the other hand, the false negative rate of FBGA was 8% (29/343). The PPV and NPV of FBGA for predicting postpartum acidosis were 50% and 91%, respectively. The sensitivity was 9% and the specificity was 99%. In a multivariate logistic regression analysis, maternal body mass index (odds ratio [OR] 1.1; 95% confidence interval [CI] 1.01–1.17; P = .029) and cardiotocography variations (OR 0.80; 95% CI 0.66–0.98; P = .029) independently affected the predictive value of FBGA. The PPV of FBGA regarding neonatal depression according to Apgar scores was low with only 17%. We conclude that FBGA may be used in clinical practice to rule out, but not to rule in, neonatal acidosis in parturients with NRFHRT. It can avoid unnecessary interventions such as cesarean section or operative vaginal delivery in up to 90% of cases, but cannot reliably detect fetal acidosis.

Non-reassuring fetal heart rate patterns in association with umbilical artery acidosis

“…[5] Although fetal scalp blood sampling and fetal oxygen saturation have been suggested to reduce this false-positive rate, these methods are invasive. [12,13] There are many reports in the literature showing that late decelerations are associated with fetal acidemia. In addition, decreased variability was suggested as an indicator of fetal acidemia.…”

Analysis of Cesarean Section Rates Based on ROBSON Classification System in a Tertiary Care Hospital in West Coast of Gujarat, India

“…In decision making in cases of suspicious CTG, fetal scalp stimulation or fetal scalp blood sampling may be used [2] . National Institute for Health and Care Excellence (NICE) guidelines agree that fetal scalp blood sampling and blood gas analysis can be an alternative tool to rule out acidosis and fetal compromise, preventing up to 90% of CS and operative interventions [3,4] . Also increase in usage of oxytocin infusion pumps reduces incidence of hyperstimulation of uterus and thus also fetal distress due to uterine hyperstimulation.…”

Usefulness of Robson classification system to analyze caesarean section deliveries: a hospital based study

“…Fetal heart rate abnormality and fetal distress are increasingly a cause for emergency CS in laboring patients. Cardiotocography has higher false positivity leading to increasing CS rate from non-reassuring fetal heart pattern and fetal distress 21 .National Institute for Health and Care Excellence (NICE) guidelines agree that fetal scalp blood sampling and blood gas analysis can be an alternative tool to rule out acidosis and fetal compromise, preventing up to 90% of CS and operative interventions 22,23 . In our centre, unavailability of the test and lack of clinical acumen poses difficulty in assessing fetal academia.…”