A direct comparison of the diagnostic accuracy of ST segment analysis (STAN) and fetal scalp blood sample lactate: A...

Fetal scalp blood sample (FBS) lactate and ST analysis (STAN) are adjuncts to cardiotocography (CTG) in high-risk deliveries, aiming to increase the specificity of the fetal monitoring. These methods have never been compared directly, through simultaneous evaluation in the same deliveries.

We conducted a prospective, population-based study on deliveries with singleton, cephalic fetuses in gestational week ≥ 36 + 0 monitored with internal CTG. Cases were defined as deliveries with umbilical cord artery pH ≤ 7.10. For each case, the following three deliveries with umbilical cord artery pH > 7.10 were included as controls. The sensitivity and specificity of FBS lactate and STAN for the predefined adverse neonatal outcomes were compared using McNemar's test.

Of 10,000 women included by passive consent, 178 deliveries were included as cases, and 516 as controls. STAN had a significantly higher sensitivity for the main outcome (pH ≤ 7.10) compared to FBS lactate (49 % vs. 40 %, p = 0.03). Although STAN showed a tendency toward a higher sensitivity for the secondary outcomes, differences were not statistically significant (p = 0.14-0.50). FBS lactate had significantly higher specificity for all outcomes (main outcome 88 % vs. 69 %, p < 0.01).

STAN demonstrated a higher sensitivity for moderate acidemia compared to FBS lactate, but with lower specificity for all outcomes. These results do not not provide evidence to support the choice of one fetal surveillance system over the other. Further research should focus on how potential advantages of either method could be combined. The study is registered in ClinicalTrials.gov (ClinicalTrials.gov identifier: NCT04779294).