Beyond the Peaks: A Guide to the Critical Importance of Uterine Relaxation Time
Whether you’re just starting to learn how to evaluate the fetal heart rate tracing or you’ve been interpreting strips for decades, the TOCO pattern is a familiar sight. We’re experts at identifying a strong contraction pattern, masters of titrating Pitocin, and composed in the face of a challenging strip. But while we focus on the strength and frequency of the peaks, are we giving enough credit to its equally important counterpart: relaxation time? This article is going to take a deeper dive into the significance of uterine relaxation time, the period of recovery that protects both the patient and fetus.
From Uterine Rest to Fetal Reassurance: A Cellular Perspective
Relaxation time is the time between the end of one contraction and the start of the next. This is the period when the uterus softens, blood flow to the placenta improves, and the fetus gets a chance to recover from the stress of the previous contraction.
The fundamental principles: during a contraction, the uterine muscle fibers constrict, temporarily reducing blood flow through the spiral arteries and leading to a transient decrease in fetal oxygenation. A healthy fetus has oxygen reserves to handle these short periods of reduced supply. However, when relaxation time becomes too short, the fetus may not have enough time to re-oxygenate.
Research shows that during the first stage of labor, an average relaxation time of 60 seconds is considered normal, whereas an average of 45 seconds is normal in second stage of labor, as contraction frequency typically increases [1]. Sustained uterine pressure during inadequate relaxation can compromise uterine blood flow, which is a known risk factor for fetal acidemia. This often shows up as changes in the fetal heart rate tracing and why clinicians closely monitor, not just contraction frequency, but the length of rest time in between.
The Art and Science of Assessing Relaxation
For every L&D nurse, assessing uterine activity is more than just counting contractions. It’s a multisensory skill that blends technology with hands-on assessment.
While the external TOCO is a valuable tool for tracking the frequency and duration of contractions, it’s unreliable for assessing intensity and resting tone. This is where our experienced hands come in. Palpating the uterus between contractions is the way to truly gauge if the uterus is returning to a soft, relaxed state.
Our First Line of Defense: Proactive Interventions
When you notice signs of inadequate uterine relaxation, there are several evidence-based interventions that can make a significant improvement. The goal is always the same: promote fetal oxygenation by reducing uterine activity.
- Position Changes: Repositioning the patient can have a profound impact on uterine perfusion. Moving from a supine to a lateral position can increase cardiac output by up to 25% [2], so encouraging a lateral position is a simple and effective intervention.
- IV Fluid Bolus: Increasing hydration can improve circulatory volume and, in turn, uteroplacental perfusion.
- Decrease or Discontinue Oxytocin or Prostaglandins: If oxytocin is infusing, this is often a crucial step. Studies on oxytocin pharmacokinetics show its half-life is about 3-6 minutes [3], meaning you can see a rapid improvement in the uterine activity pattern after stopping the infusion. Holding misoprostol or Cervidil will also promote uteroplacental perfusion.
A Renewed Focus on Relaxation Time
As L&D nurses, our expertise lies in our ability to see the whole picture; to interpret the subtle cues from both patient and fetus. By placing a renewed emphasis on uterine relaxation time, we can proactively protect the well-being of our smallest patients. The relaxation time between contractions isn’t just a moment of rest. It’s a critical period of recovery that is fundamental to a safe and healthy birth.
OBIX Uterine Activity (UA) Tool
The OBIX System’s E-Tools were developed in collaboration with Lisa Miller, CNM, JD, to support OB providers during the assessment of the Fetal Heart Rate (FHR) and Uterine Activity (UA) in labor.
The UA Tool presents key information during the evaluation and management of uterine activity during labor. This tool will display contraction frequency, duration and relax time when utilizing TOCO, based on a 10-, 15-, 30-, or 60-minute segment as defined by the user. Additionally, uterine contraction intensity, duration, resting tone, and MVUs are displayed when an IUPC is in place.
FEATURES
- Allows clinicians to confirm tool evaluation results or make modifications based on their assessments. Able to define segment start in the emphasized area.
- Able to add, reposition, or remove contractions.
- Supports TOCO or IUPC monitoring modes.
- Can be used in active and archived traces.
- Uterine contraction assessment information can be added to the patient chart in a single click.
BENEFITS
- Accurate measurements for identifying uterine contraction frequency, intensity, and duration.
- Supports patient safety initiatives related to uterine activity management and assessment and reduction of cesarean rate.
- Clarify confusion regarding proper documentation and evaluation of contractions, while strengthening the clinician’s skills.
- Allows for more accurate and appropriate use of Pitocin.
About Clinical Computer Systems, Inc.
For 30 years, Clinical Computer Systems, Inc. (CCSI) has been dedicated to the support and development of the OBIX® Perinatal Data System, a clinically driven platform purpose-built for labor and delivery.
The OBIX System is designed to help support confident decision-making, help improve communication across care teams, and help protect the outcomes that matter most: healthy moms and healthy babies.
CCSI partners with clinicians and customers to continuously advance OBIX solutions, adapting to regulatory, technology, and industry changes while supporting hospitals clinical, operational, and strategic goals.
Visit OBIX.com and follow us on LinkedIn, Facebook, and Instagram.
References
[1] Bakker PCAM, Kurver PHJ, Kuik DJ, et al. Elevated uterine activity increases the risk of fetal acidosis at birth. Am J Obstet Gynecol 2007; 196;313.e1-313.e6.
[2] Soma-Pillay P, Nelson-Piercy C, Tolppanen H, Mebazaa A. Physiological changes in pregnancy. Cardiovasc J Afr. 2016 Mar-Apr;27(2):89-94. doi: 10.5830/CVJA-2016-021. PMID: 27213856; PMCID: PMC4928162.
[3] Uvnäs-Moberg K. The physiology and pharmacology of oxytocin in labor and in the peripartum period. Am J Obstet Gynecol. 2024 Mar;230(3S):S740-S758. doi: 10.1016/j.ajog.2023.04.011. Epub 2023 Jul 13. PMID: 38462255.
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The material presented in this blog represents the opinion of the author(s) and not necessarily the views of Synova Associates. Synova Associates does not endorse any specific products or organizations but strives to connect its industry partners with leaders interested in product/educational innovation.
