Analysis of deceleration area of fetal heart rate during the second stage of labor and its relation to acidaemia at delivery.

Objective To determine the value of deceleration area of fetal heart rate as indicator of low arterial pH and a significative fetal distress during the second stage of labor. Study design A retrospective analysis of deceleration area of fetal heart rate recordings in 171 women with a physiologic pregnancy, was performed for the last hour preceding delivery. All the pregnancies progressed to term and did not require induction of labor. The deceleration area was calculated, after digital analysis, with Autocad System 2004 with FHR from 140 to 120 bpm. The accordance analysis and the quantification of threshold value of the deceleration area, indicative of fetal acidaemia, were calculated by unvaried (linear regression) analysis with statistical significance set at p < 0.05. Results Stepwise and multiple regression analysis showed a statistical significant association between umbilical artery pH, Hct, PO2, PCO2 and SO2 at birth used as the dependent variable and the deceleration area, calculated at 140 bpm, at 130 bpm and 120 bpm, in the last 60 and 30 minutes of labor, used as the indipendent variable. Stepwise regression showed that the number of deceleration had an indipendent statistically significant association with umbilical artery pH and Hct. The quantification study of threshold value of deceleration area, indicative of fetal acidaemia, evidenced that during an antenatal fetal heart rate, recorded for 60 and 30 minutes before delivery, total deceleration area was ”d84.41 cm2 and ”d60.12 cm2 for FHRb at 140 bpm, ”d73.93 cm2 and ”d44.36 cm2 for FHRb at 130 bpm and ”d35.50 cm2 and ”d32.22 cm2 for FHRb at 120 bpm (p < 0.001). Conclusion We propose a new and very simple methodological approach to support classical cardiotocography which will be able not only to calculate the cut-off of fetal wellbeing at each FHRb, but also let us know about the fetus capacity to compensate any hypoxical insult.