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.