13 Introduction Antenatal CTG Some pregnancies may be complicated by a medical condition in the mother or a condition that may affect the health or development of the baby. Although there is no clear evidence that aCTG improves perinatal outcomes31, guidelines generally recommend the use of aCTG to assess fetal well-being during pregnancy in women at increased risk of complications.32-35 The CTG, a continuous electronic recording of the fetal heart rate, is obtained through an ultrasound transducer placed on the mother’s abdomen. A second transducer is placed on the mother’s abdomen to record any uterine activity. The maternal pulse is monitored using a finger probe. The fetal heart rate, maternal pulse, and uterine activity are monitored simultaneously.31 Antenatal CTG is most commonly performed in the third trimester of pregnancy (after 28 weeks). The underlying theoretical concept for the use of aCTG is that it is a test to identify babies with chronic hypoxia or at risk of developing chronic hypoxia.36 An ideal test has both high specificity and high sensitivity (100%). CTG has a high sensitivity (95%) but a low specificity (20%).36 This means that CTG can correctly identify a fetus not at risk, but in the case of a non-reassuring CTG, a large number of fetuses will show abnormalities on the CTG without being at risk of chronic hypoxia. However, if CTG is performed and interpreted as non-reassuring, this may lead to further action (further testing, hospital admission, induction of labor, or cesarean section).31 The introduction of ultrasound and electronic fetal monitoring in the 1970s contributed to a shift in emphasis from mainly maternal outcomes to both maternal and fetal outcomes.37 Concerns about the role of electronic fetal monitoring in the rising rates of cesarean section in high-income countries were raised about a decade after its introduction.37 One of the main disadvantages of the CTG is that there is substantial variation in the interpretation of CTG patterns. Several classification systems exist to classify CTG patterns, of which the International Federation for Gynecology and Obstetrics (FIGO) guidelines are probably the most widely accepted. Previous research on CTG assessment has shown variation between groups of healthcare professionals in obstetrician-led care.38 Although the interobserver agreement in the assessment of reassuring aCTGs is fair to good, low interobserver agreement was found for non-reassuring aCTGs.39,40 There is also variation in the assessment of the different CTG components: baseline heart frequency, accelerations, and contractions showed good to excellent interobserver agreement in aCTG assessment, whereas other CTG components such as variability and the number of decelerations did not.38,39,41 The baseline, variability, accelerations, and decelerations components all showed higher levels of intraobserver agreement than interobserver agreement.42 1
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