Reliability of fetal cardiotocography in predicting baby's condition at birth

Abstract

RATIONALE: Currently the most commonly used Antenatal and Intrapartum test of fetal well being is cardiotocography (CTG). Although it has gained popularity because of easy application and documentation, its use has caused an increase in medical intervention (caesarean and instrumental vaginal deliveries) without any decrease in perinatal morbidity or mortality. Objective: To ascertain the reliability of CTG in predicting or detecting fetal hypoxia. Settings: Four antenatal wards at De Soysa Maternity Hospital and one antenatal ward at North Colombo Teaching Hospital. Methods: All Pregnant mothers (n = 1246) having periods of amenorrhoea (POA) of 37 to 41 weeks who underwent at least one C.T.G within one hour of emergency delivery or within 24hours of elective delivery during the period of August 2002 to January 2003 at DMH (n - 895), and July to October 2003 at North Colombo Teaching Hospital (n =360) were included in this study. Subjects with severe fetal growth restriction (< 5 ' centile for POA) and severe pregnancy induced hypertension (systolic BP >160 mm Hg and Diastolic BP >110mmHg with or without proteinuria or impending eclamptic signs) were excluded from the study. CTG was recorded for 20 minutes using either Sonicaid or Toitu machines. Sensitivity, specificity, negative predictive value, positive predictive value and accuracy were calculated with regard to ability of the CTG to detect or exclude fetal hypoxia. Fetal hypoxia was defined as: Apgar score <7 at 5minutes of birth and / or baby needing intermittent positive pressure ventilation at birth and / or presence of moderate / thick meconium at the onset of labour and /or appearance of meconium during labour. RESULTS: Of the 1246 babies delivered within 24 hours of the CTG, 141 (12.1%) had fetal hypoxia. The CTG had a sensitivity of 57%, specificity of 90.5%, positive predictive value of 44%, negative predictive value of 93.9% and an accuracy of 86% in detecting or predicting fetal hypoxia. Conclusion: The CTG has a high rate of false positive and a low rate of false negatives. Its sensitivity of 57.6% makes it unsuitable as a screening test. Other reliable indicators should be sought.