Second stage fetal heart rate patterns and neonatal acid-base status

Background: Fetal surveillance in labour is performedmostly to identify fetuses at risk of hypoxia in order toreduce neonatal morbidity and mortality by initiatingtimely intervention. While normal and abnormal fetalheart rate (FHR) patterns have been well recognisedand characterized for the first stage of labour, FHRpatterns during the second stage of labour commonlyshowed some forms of abnormalities leading to problemsin interpretation, particularly in predicting fetal hypoxiaand acidosis. This study aims to identify patterns of FHRtracing during the second stage of labour associated withneonatal acidosis.Methods: A prospective cross sectional study wasconducted in the Labour Ward of a state referral hospital.The study population were patients with low-risksingleton pregnancies between 37 to 42 weeks gestationwho had normal cardiotocograph (CTG) tracing in thefirst stage of labour. CTG was recorded during the secondstage of labour and neonatal umbilical cord blood wasobtained for acid-base analysis immediately after birthprior to the delivery of placenta. FHR patterns weregrouped according to modified Melchior and Barnard’sclassification and matched with neonatal acid-basestatus. Patients with normal FHR pattern in the secondstage acted as control.Results: A total of 111 matched pairs were analysed.Ninety nine (89.2%) second stage FHR tracings showedabnormal features when compared to control. There weresignificantly more neonatal acidosis and hypercapniain type 1b, type 2a, type 2b and type 3 CTG patternscompared to control, in increasing order of severity. Inaddition, types 2b and 3 showed significant difference inthe base excess.Conclusion: Certain second stage fetal heart ratepatterns were found to be associated with neonatalacidosis.