Association between different types and characteristics of fetal deceleration during labour and neonatal acidemia at delivery: A case-control study

Objective: Classification of fetal heart rate (FHR) decelerations as suspicious or pathological differs between current interpretation templates for intrapartum cardiotocography. Decelerations are the most frequent FHR pattern irregularities during labour. The aim of this study was to assess the association between different types and characteristics of decelerations and acidemia at birth. Methods: This case-control study includes 365 cases with cord pH < 7.10 after 1st stage cesarean delivery or pH < 7.05 after vaginal delivery at > 34 + 0 weeks after induced or spontaneous labour, and 730 controls with pH ≥ 7.15. Cardiotocographic recordings from 60 min before birth were scrutinized and decelerations evaluated in detail. Odds ratios (OR) with 95 % confidence intervals for acidemia at birth were determined. Results: The following types of decelerations were associated with acidemia: Late decelerations; OR 9.0 (6.1-13) if > 5, and OR 19 (9.7-37) if repetitive > 20 min, combined decelerations; OR 4.2 (2.7-6.4) if > 5 and OR 6.4 (3.1-13) if repetitive > 20 min, one prolonged deceleration > 5 min; OR 12 (7.9-19), three prolonged decelerations for 3-5 min; OR 10 (4.3-25), and > 5 variable decelerations > 60 s; OR 2.2 (1.6-2.9). For variable decelerations > 60 s, absent variability within decelerations was the only additional characteristic significantly associated with acidemia; OR 5.8 (2.1-16). A strong association with acidemia was noted for a FHR below the baseline ≥ 50 % of the time > 30 min; OR 14 (10-19). Conclusion: Late and prolonged decelerations are strongly, and combined decelerations moderately associated with acidemia. The risk of acidemia is highly increased if FHR is below baseline ≥ 50 % of the time.