Intrapartum Fetal Heart Rate Tracing Among Small-for-Gestational Age Compared With Appropriate-for-Gestational-Age Neonates

OBJECTIVE: To compare fetal heart rate (FHR) patterns during the last hour of labor between small-for-gestational-age (SGA; birth weight less than the 10th percentile for gestational age) and appropriate-for-gestational-age (AGA; birth weight at the 10-90th percentile) neonates at 36 weeks of gestation or greater. We also compared the rate of cesarean delivery and composite neonatal morbidity among SGA and AGA newborns.

METHODS: This is a secondary analysis of a randomized trial of intrapartum fetal electrocardiographic ST-segment analysis. We excluded women with chorioamnionitis, insufficient duration of FHR tracing in the hour before delivery, and anomalous newborns. Fetal heart rate patterns were categorized by computerized pattern recognition software (PeriCALM Patterns). Composite neonatal morbidity was defined as any of the following: intrapartum fetal death, Apgar score 3 or less at 5 minutes, cord artery pH 7.05 or less, base deficit 12 mmol/L or greater, neonatal seizure, intubation at delivery, neonatal encephalopathy, and neonatal death. Logistic regression was used to evaluate the association between FHR patterns and SGA adjusted for magnesium sulfate exposure and stage of labor.

RESULTS: Of the 11,108 women randomized, 85% (n=9,402) met inclusion criteria, of whom 9% were SGA. In the last hour, the likelihood of accelerations was significantly lower among SGA than AGA neonates (72.4% vs 66.8%; P=.001). Variable decelerations lasting greater than 60 seconds, with depth greater than 60 beats per minute (bpm) or nadir less than 60 bpm, were significantly more common with SGA than AGA (all P<.001). The rate of late decelerations, prolonged decelerations, or bradycardia were similar between SGA and AGA (all P>.05). Cesarean delivery for fetal indications was significantly more common with SGA (7.0%) than AGA (4.0%; P<.001). The composite neonatal morbidity was 1.4% among SGA and 1.0% among AGA (odds ratio 1.40, 95% CI 0.74-2.64).

CONCLUSION: Although the FHR patterns in the last hour of labor differ among SGA and AGA neonates, as does the rate of cesarean delivery, the composite neonatal morbidity was similar.