Intrapartum fetal heart rate between 150 and 160 bpm at or after 40 weeks and labor outcome.

Abstract

A baseline fetal heart rate between 110 and 160bpm is considered normal. However, among normal fetuses the average baseline heart rate has been shown to diminish progressively and the 90th centile of the fetal heart rate at 40weeks of gestation has been consistently found at around 150bpm. The aim of our study was to assess the labor and neonatal outcome of fetuses at 40 gestational weeks or beyond, whose intrapartum baseline fetal heart rate was between 150 and 160bpm. Retrospective cohort study including singleton pregnancies with spontaneous onset of labor, gestational age between 40+0 and 42+0 weeks, category I CTG trace according to the FIGO guidelines 2015 with baseline fetal heart rate between 110 and 160bpm during the first 60minutes of active labor. Exclusion criteria were maternal hyperpyrexia at admission, fetal arrhythmias, maternal tachycardia (>110bpm) and uterine tachysystole (>5 contractions/10minutes). The following outcomes were compared between fetuses with a baseline ranging between 110 and 149bpm and those with a baseline ranging between 150 and 160bpm: incidence of meconium-stained amniotic fluid, intrapartum hyperpyrexia, mode of delivery, Apgar at 5 minutes<7, arterial pH<7.1 and Neonatal Intensive Care Unit admission, incidence of a composite adverse neonatal outcome. In all, 1004 CTG traces were included in the analysis, 860 in Group 110-149bpm and 144 in Group 150-160 bpm. Group 150-160bpm had a significantly higher incidence of meconium-stained amniotic fluid (odds ratio [OR] 2.6; 95% CI 1.8-3.8), maternal intrapartum hyperpyrexia (OR 4.7; 95% CI 1.1-14.6), urgent/emergent cesarean section for suspected fetal distress (OR 13.4; 95% CI 3.3-54.3), Apgar<7 at 5th min (OR 9.13; 95% CI 1.5-55.1) and neonatal acidemia (OR 3.5; 95% CI 1.5-55.1). Logistic regression including adjustiing for potential confounders showed that fetal heart rate between 150 and 160bpm is an independent predictor of meconium-stained amniotic fluid (adjusted odds ratio [aOR] 2.2; 95% CI 1.5-3.3), cesarean section during labor for fetal distress (aOR 10.7; 95% CI 2.9-44.6), neonatal acidemia (aOR 2.6; 95% CI 1.1-6.7) and adverse composite neonatal outcome (aOR 2.6; 95% CI 1.2-5.6). In fetuses at 40weeks or beyond, an intrapartum fetal heart rate baseline ranging between 150 and 160bpm seems associated with a higher incidence of labor complications.