Fetal heart monitoring: mild, moderate, and severe decelerations

The first column in this series reviewed standard electronic fetal monitoring (EFM) definitions and categories proposed by the National Institute of Child Health and Human Development (NICHD).¹ The second reviewed the evidence underlying atypical variable decelerations. This column will explore the evidence behind the classification of decelerations as mild, moderate, and severe.

Published evidence will be stratified according to the method outlined by the US Preventive Services Task Force (USPSTF), summarized in the Table.²

Furthermore, it did not attempt to control for important confounding factors such as the presence or absence of normal baseline rate, moderate variability, or accelerations. Consequently, evidence from this study does not qualify as Level I or Level II.

Subsequently, Krebs reported 5-minute Apgar scores <7 in 8.3% of newborns with severe variable decelerations in the last 30 minutes of monitoring compared with only 3.4% of newborns with mild or moderate decelerations.⁵ This study did not control for baseline rate, moderate variability, or accelerations, and did not evaluate newborn acid-base status. Therefore, the evidence does not meet the USPSTF definition of Level I or Level II.

Newborn outcomes in 1,859 term pregnancies were the focus of a study by Berkus.⁷ When accelerations were present, deceleration categories had no differential impact on 5-minute Apgar scores <7 or umbilical artery pH values <7.15. This study did not control for baseline rate or variability, and did not differentiate between respiratory and metabolic acidemia.

Kazandi studied 96 singleton pregnancies and reported that mild, moderate, and severe decelerations were associated with progressively higher rates of 5-minute Apgar scores <7 and umbilical artery pH values <7.2.⁸ However, this study also failed to control for baseline rate, variability, and accelerations, and did not distinguish respiratory from metabolic acidemia.