Relationship between Deceleration Areas in the Second Stage of Labor and Neonatal Acidemia

Understanding the fetal heart rate (FHR) in the second stage of labor is important to recognize critical clinical outcomes. During this time, fetus is subject to head compression that activate baroreceptor reflexes that cause FHR deceleration. Large deceleration areas (DA: measured as duration by depth), have been associated to critical fetal outcomes. A preliminary study on 33 pregnant women reported a significant inverse correlation between DA in the last 60 minutes before delivery and umbilical pH at birth (fetal-distress measure when < 7.1). The aim of this study is to further characterize the relationship between DA in the last 60 minutes before delivery and pH at birth on a larger population. Thus, 433 FHR recordings from the 'CTU-CHB Intrapartum Cardiotocography Database' of Physionet were used. Signals were classified as Cases (pH < 7.1) and Controls (pH > 7.1). Results confirmed that Cases have significantly higher DA than Controls (5.32 cm2 vs 1.44 cm2; P < 0.05). The inverse correlation between DA in the last 60 minutes before delivery and pH at birth, was weak but significant (ρ=-0.23, P<10-6). Thus, results confirm that critical fetal outcomes increase with increasing acidemia; however, such relationship may not be strictly linear. Future studies are focused on discrimination of fetal distress using DA.