Aim: The aim of this study was to clarify the association between fetal heart rate (FHR) tracing interpretation levels in the second stage of labor and poor fetal acid-base balance.
Material and methods: The database at one tertiary hospital in Nagoya, Japan, was retrospectively reviewed for women with singleton fetuses in cephalic presentation and vaginal labor at ≥37 + 0 gestational weeks between 1 June 2011 and 30 April 2012. Continuous FHR tracings in the second stage of labor were subdivided into 15-min intervals, each of which we called a window, from the beginning of labor through delivery, and were assessed according to the five-tier classification proposed by the Japan Society of Obstetrics and Gynecology, in which level 1 is normal, level 2 is subnormal, and levels 3-5 are abnormal patterns.
Results: In total, 777 parturient women were eligible for the study protocol. The numbers of women with maximal levels of 1, 2, 3, 4, and 5 were 3, 77, 341, 349, and 7, respectively. No cases of severe fetal acidosis (pH < 7.0 or base excess <-12 mmol/L) were recorded when the maximal levels were below 3. Both the pH and base excess of the umbilical artery decreased with higher levels of FHR tracings interpretation (P < 0.001). Both the summations of level-4 windows and level-3 and level-4 windows were significantly higher in women with severe fetal acidosis than in women without (P < 0.001), indicating that the duration of abnormal levels is associated with severe fetal acidosis.
Conclusions: Both the degree and duration of FHR tracing abnormalities correlate with severe fetal acidosis.
Keywords: acid-base balance; fetal heart rate tracing; five-tier classification; second stage of labor; severe acidosis.
© 2014 The Authors. Journal of Obstetrics and Gynaecology Research © 2014 Japan Society of Obstetrics and Gynecology.