Corresponding Author Contact Information:
Rebecca Rimsza, MD
Department of Obstetrics and Gynecology, Washington University School of
Medicine
660 S. Euclid Ave, Box 8064, St. Louis, MO 63110.
e-mail: rimsza@wustl.edu phone: 520-981-0933
Short Title: Intrauterine resting tone and neonatal outcomes
Title: 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
Keywords: Labor, Neonatal Outcomes, Intrauterine pressure,
Intrauterine tone, Baseline tone
Tweetable Abstract
Elevated intrauterine resting tone is during labor associated with
increased risk of neonatal morbidity
Introduction
Contraction monitoring during labor
is critical to assessing the clinical response to labor induction.
Evaluating uterine response to oxytocin allows for safe titration to
achieve cervical dilation. There are three main strategies for
contraction monitoring: manual palpation, external tocodynamometry and
intrauterine pressure catheter (IUPC). Manual palpation can vary based
on provider experience and maternal body habitus. An external tocometer
allows for monitoring of contraction frequency and is non-invasive but
does not provide an assessment of contraction magnitude which may be
critical when determining need for cesarean delivery due to failure to
progress. Internal contraction monitoring using an IUPC is more invasive
and requires rupture of membranes prior to use.
However, an IUPC offers additional
advantages over tocodynamometry, most importantly, an objective
measurement of intrauterine baseline and contraction-induced pressure,
allowing for a more quantitative assessment of uterine contractility.
Prior to placement, the IUPC is calibrated outside the uterus, with
external atmospheric pressure set as baseline or zero. Once placed
inside the uterus, the IUPC will report a baseline pressure within the
uterus between contractions (resting tone) and a peak intrauterine
pressure when the uterus is maximally contracted. The difference between
these two values calculated over a ten-minute period is considered the
contraction pressure and is measured in Montevideo units (MVU)[1].
Prior research has focused on the impact of maximum tone and MVUs on
labor duration and cervical dilation [2-4]. The potential neonatal
effects of elevated baseline intrauterine pressure are unknown, but
prior studies have shown that uterine contractions compress the spiral
arteries, resulting in placental and fetal hypoxia [5, 6].
We
hypothesized that elevated intrauterine resting tone could lead to
compression of the spiral arteries, thus limiting uterine blood flow and
resulting in neonatal compromise. Therefore, our objective was to assess
the association between elevated resting tone during labor and neonatal
morbidity.