25 Observer agreement of aCTG assessments they received an online set of 10 aCTGs with additional information about the indication for the aCTG, the woman’s pregnancy details, relevant medical history, and a scoring form to assess the aCTGs. The participants could assess the aCTGs after informed consent at a time and place convenient to them. The aCTG traces of healthy women with specific indications for aCTG (reduced fetal movements, external cephalic version, or postdate pregnancy) were obtained from the wireless portable CTG-system Sense4Baby.17 The aCTG traces were at least 30min and the paper speed was 2cm/min. We used two sets of 10 aCTG traces each to ensure a representative sample. Each set was assessed by at least five assessors per professional group. The participants were asked to assess the same 10 aCTGs twice, in a different order, at a 1-month interval (see Appendix A1 for sample size considerations). All aCTG assessments were conducted independently, that is, assessors were blinded to the results of other assessors. In the study, for the aCTG assessment, we used a classification system based on the FIGO classification (Figure 1). Although this classification is developed for intrapartum CTG, the Dutch Federation of Obstetrics and Gynecology also recommends using it for aCTG.18 The adapted classification system for various components and overall classification was provided to the assessors. Antenatal CTG classification CTG classification Baseline Heart Frequency (bpm) Accelerations and variability Decelerations Contractions Reassuring: The CTG complies with all criteria 110-150 Minimal two accelerations in a 45-minute CTG tracing Variability 5-25 bpm Absence of decelerations Maximum of two contractions per 10 minutes Absence of hypertonia Non-reassuring: The CTG deviates from one or more criteria <110 or >150 < two accelerations in a 45-minute CTG tracing Variability <5 or > 25 bpm Presence of 1 or more decelerations >two contractions per ten minutes Presence of hypertonia CTG, cardiotocography; bpm, beats per minute. Figure 1: Antenatal CTG classification system used in the study STATISTICAL ANALYSIS The analyses were performed using SPSS statistics 28.0 and Rstudio 2021.09.1. The baseline characteristics of the study population were analyzed using descriptive 2
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