OBJECTIVE: To describe the incidence and characteristics of terminal fetal heart rate decelerations and to estimate their association with acidemia.
METHODS: A 5-year retrospective cohort study of all women with singleton, nonanomalous gestations who labored and reached complete dilation at or after 37 weeks of gestation. The 30 minutes of electronic fetal monitoring before delivery were interpreted by two formally trained research nurses, blind to clinical data, using American College of Obstetricians and Gynecologists guidelines. Terminal decelerations (decelerations without recovery of 120 seconds or more) defined the exposure. Terminal bradycardia (10 minutes or more) was secondarily explored. Univariable and multivariable analyses were performed to estimate risk of acidemia (umbilical cord gas arterial pH level 7.10 or less).
RESULTS: Of 5,388 women meeting inclusion criteria, 951 (17.7%) experienced a terminal deceleration whereas 4,437 (82.3%) did not. The incidence of acidemia among the 951 women with a terminal deceleration was low (1.3%; n=12). However, acidemia (adjusted odds ratio [OR] 18.6; 95% confidence [CI] 5.0–68.9) and higher-level nursery admission (adjusted OR 5.4; 95% CI 1.9–15.3) were more likely if the terminal deceleration was 10 minutes or more. Terminal decelerations were longer among neonates with acidemia (6.7 minutes compared with 3.2 minutes; P<.01). For every additional 120 seconds of duration beyond the first 120 seconds, there was a corresponding decrease in umbilical cord gas pH level by 0.042 (95% CI 0.040–0.048; P<.01).
CONCLUSIONS: More than 98% of term fetuses with terminal decelerations deliver with normal umbilical cord gas pH levels. However, bradycardia is associated with increased risk of acidemia and higher-level nursery admission. This information can be incorporated into clinical decision-making regarding urgency of delivery.
LEVEL OF EVIDENCE: II