Association of fetal heart rate short term variability pattern during term labor with neonatal morbidity and small for gestational age status

Objective: To assess the association of fetal heart rate short-term variability (STV) pattern during term labor with both neonatal composite morbidity (cord blood pH < 7.10 and/or neonatal intensive care unit admission and/or Apgar score at 5 min <7) and small for gestational age (SGA) status.Study design: Retrospective cohort in a single academic institution between January 2016 and December 2018. A total of 1896 women that delivered a singleton during labor in cephalic presentation after 37 weeks of gestation were included (948 women with SGA neonates and 948 women with appropriate weight for gestational age (AGA) neonates that were matched to women with SGA neonates based on maternal age, parity, induction of labor, gestational diabetes, gestational age at delivery and a history of one cesarean section using propensity score matching). STV was compared at labor onset (cervical dilation < 4 cm), in the first stage of labor (cervical dilation = 6 cm) and in the second stage of labor (cervical dilation = 10 cm). A generalized linear mixed model was used to assess the association between SGA status, neonatal composite morbidity and STV.Results: After adjustment for maternal origin, term, gestational diabetes, labor length, SGA status was not associated with any change in STV during labor (mean adjusted STV:-0.20 ms, 95 %CI[-0.58-0.17], p = 0.284 at labor onset, 0.29 ms, 95 %CI[-0.1- 0.68], p = 0.155, in the first stage of labor and 0.36 ms, 95 %CI [-0.02-0.74], p = 0.065 in the second stage of labor). In case of neonatal composite morbidity mean adjusted STV was lower in the first stage of labor (mean adjusted STV:-1.29 ms, 95 %CI[-2.1 --0.43], p = 0.003) and in the second stage of labor (mean adjusted STV:-1.15 ms, 95 %CI[-1.96 --0.34], p = 0.005). The results were similar with the addition of delivery mode and meconium-stained amniotic fluid in the model or non-reassuring fetal heart rate and meconium-stained amniotic fluid. Conclusions: This work suggests that STV decrease during term labor is associated with fetal well-being, inde-pendently of fetal weight. This suggests that further prospective studies should consider the evaluation of this parameter in the prediction of neonatal compromise.