Association between elevated intrauterine resting tone during labor and
neonatal morbidity: A secondary analysis of a prospective cohort study
Abstract
Objective: Internal contraction monitoring during the course of labor
may identify elevated intrauterine resting tone. Our objective was to
assess the association between elevated resting tone during labor and
neonatal morbidity. Design: Secondary analysis of a prospective cohort
study. Setting and Population: Term singleton patients with ruptured
membranes and an intrauterine pressure catheter in place: Tertiary care
hospital, United States of America Methods. Intrauterine resting tone
was calculated as the average baseline pressure between contractions.
The study group had elevated intrauterine resting tone, defined as
intrauterine resting tone ≥75th percentile. Main Outcome Measures:
Composite neonatal morbidity: hypoxic ischemic encephalopathy,
hypothermia treatment, intubation, seizures, umbilical arterial pH ≥
7.1, oxygen requirement, or death. Results: Of the 8580 patient in the
cohort, 2210 (25.8%) were included. The median intrauterine resting
tone was 9.7 mmHg (IQR 7.3-12.3 mmHg). Elevated resting tone was
associated with shorter median duration of the first stage of labor
(10.0 hrs vs 11.0 hrs, p <0.01) and lower rates of labor
induction (p < 0.01). Neonatal composite morbidity was higher
among patients with elevated intrauterine resting tone (5.1% vs 2.9%,
p=0.01). After adjusting for chorioamnionitis and amnioinfusion,
elevated intrauterine resting tone was associated with increased risk of
neonatal morbidity (aOR 1.70, 95% CI 1.06-2.74). Compared to normal
tone, elevated intrauterine resting tone was associated with mild
acidemia and elevated lactate (aOR 1.81, 95% CI 1.38-2.37 and aOR 1.45,
95% CI 1.17-1.80, respectively). Conclusion: Elevated intrauterine
resting tone is associated with increased risk of neonatal composite
morbidity. Funding: None