Frequency of fetal heart rate categories and short-term neonatal outcome.

OBJECTIVE: To estimate the time spent in each fetal heart rate category during labor and during the last 2 hours before delivery in term singleton pregnancy and to estimate the relationship between the time spent in each category and short-term neonatal outcomes.
METHODS: This study reviewed fetal heart rate data and newborn outcomes of women in term labor in 10 hospitals over 28 months. Fetal heart rate characteristics were assessed by labor and delivery nurses, and categories were assigned by computer using definitions from the Eunice Kennedy Shriver National Institute of Child Health and Human Development. The duration of time in each category was calculated and correlated with newborn outcome.
RESULTS: Forty-eight thousand four hundred forty-four patients were identified. Considering all of labor, category I was present 77.9% of the time, category II was present 22.1% of the time, and category III was present 0.004% of the time. In the last 2 hours before delivery, category I decreased to 60.9% of the duration, category II increased to 39.1%, and category III increased to 0.006%. Newborns of women whose last 2 hours were exclusively category I did well; only 0.6% had 5-minute Apgar scores less than 7, and 0.2% had low Apgar scores with neonatal intensive care unit (NICU) admission. When more than 75% of the last 2 hours was category II, low 5-minute Apgar score increased to 1.3% of patients, and low 5-minute Apgar score with NICU admission increased to 0.7% (both P<.001).
CONCLUSION: Category I and category II fetal heart rate patterns are common in labor, and category III patterns are rare. Increasing time in category II in the last 2 hours of labor is associated with increased short-term newborn morbidity. LEVEL OF EVIDENCE: III.