Evaluation of the discrepancy between pH and lactate in combined fetal scalp blood sampling.

Objective: To evaluate the rate of discrepancy between pH and lactate values in fetal blood sampling (FBS). To evaluate differences in obstetric management in response to combined tests (pH and lactate) and single tests (pH or lactate).

Design: Descriptive study.

Setting: Uppsala University Hospital, Sweden.

Population: Labors monitored by FBS during one year (n=241).

Methods: Discrepancy in the combined tests was defined as a test having one abnormal and one normal value. Abnormal pH was defined as 7.24 or lower and abnormal lactate as 4.2 or higher. The results were categorized according to whether the test was normal or abnormal and according to whether it was a combined or single analysis.

Main Outcome Measures: Discrepancy between pH and lactate values in combined tests. Frequency of operative delivery for fetal distress (ODFD). Time interval from the last FBS to ODFD.

Results: In the combined tests with abnormality, a discrepancy between pH and lactate values occurred in 55%. The mean time interval from the last FBS to ODFD was longer in combined tests with one abnormal compared with two abnormal test results, 75 vs. 37 minutes (p<0.05). Operative delivery for fetal distress was performed less often after combined tests than after single tests: 41/62 (66%) vs. 19/20 (95%) (p<0.05).

Conclusion: In the combined test, discrepancies were common and occurred in half of the samples with an abnormality. Obstetric management was influenced by the discrepancy between test results with respect to ODFD rates and the time interval from the last FBS to delivery.