Evaluating the diagnostic accuracy of fetal scalp blood sampling: A retrospective cohort study

Fetal scalp blood sampling (FSBS) can be used as an adjunctive test, in the presence of a pathological intrapartum fetal heart rate trace, to provide evidence of fetal acidaemia. The role of FSBS remains controversial, this study evaluates the diagnostic accuracy of FSBS at determining various adverse neonatal outcomes.

A retrospective cohort analysis of FSBS undertaken < 1 h from birth in a single UK centre in 2016 and 2017. An FSBS pH of < 7.20 was abnormal. Adverse outcomes were: low umbilical cord artery (UCA) pH (<7.20), neonatal acidaemia (UCA pH < 7.05), and 5-minute Apgar score < 7. Regression was performed to adjust for potential confounding variables. Receiver operator characteristic (ROC) curves were calculated and test accuracy, including sensitivity and specificity were determined, for an abnormal FSBS pH and adverse neonatal outcomes.

Data from 407 births occurring ≤ 60 min from FSBS were analysed. To predict neonatal acidaemia, FSBS had an area under the ROC (AUROC) of 0.77 (95 % CI 0.65, 0.88). To predict low Apgar scores, FSBS had an AUROC of 0.80 (95 % CI 0.70, 0.90). In general, an FSBS pH of < 7.20 has low sensitivity and high specificity for neonatal acidaemia (28.6 % and 85.5 % respectively) and for low Apgar scores (38.1 %, 90.82 %).

As FSBS has high specificity for adverse neonatal outcomes, it could be used to exclude asphyxia as it has a high NPV. Further research is required to evaluate whether other means of FSBS assessment, e.g. lactate, have better diagnostic test accuracy.