Monitoring uterine activity is a common practice during pregnancy and labor to assess uterine contractions. It offers a visual representation of the uterus’s work, providing important insights into labor progression and the well-being of both the birthing person and the baby. This monitoring helps healthcare providers understand uterine activity patterns for effective labor management.
How Contractions Are Detected on the Monitor
External monitoring of uterine contractions typically uses a device called a tocodynamometer, often referred to as a toco. This non-invasive sensor is placed on the abdomen, over the uterus, and secured with a belt. The toco contains a pressure sensor that detects changes in the tension of the abdominal wall as the uterus tightens and relaxes during a contraction.
When the uterine muscle contracts, it becomes firmer and pushes against the toco, which then converts this mechanical pressure into an electrical signal. This signal is sent to a monitor, where it is displayed as a waveform. This external method provides qualitative information about contraction frequency and duration, but it does not precisely measure the actual intensity or strength of the contraction.
Interpreting the Contraction Waveform
On a monitor, a uterine contraction appears as an upward curve, resembling a hill. The horizontal axis of the monitor strip represents time, marked with time intervals. The vertical axis indicates the relative intensity of the contraction.
Each contraction waveform shows a gradual rise, known as the increment or onset, as the uterus begins to tighten. It then reaches a peak, called the acme, which represents the strongest point of the contraction. Following the peak, there is a gradual fall, or decrement, as the uterus relaxes, eventually returning to a resting baseline. Healthcare providers assess the frequency of contractions by measuring the time from the start of one contraction to the start of the next. The duration of a single contraction is measured from its beginning, through its peak, to its end.
Distinguishing Contraction Types on the Monitor
The visual characteristics on the monitor help differentiate between Braxton Hicks and true labor contractions. Braxton Hicks contractions, often called “practice contractions,” are irregular in frequency, duration, and intensity. On the monitor, they appear as inconsistent, low-amplitude waves that do not follow a predictable pattern of getting closer together or stronger. They usually subside with changes in activity or position.
In contrast, true labor contractions show a more organized and progressive pattern on the monitor. They become regular, increasing in frequency, duration, and intensity over time. The waveforms for true labor contractions show clear, rising peaks that become more prominent and closer together as labor progresses. Unlike Braxton Hicks, true labor contractions do not go away with movement or position changes; in fact, they may become stronger.
What Monitoring Information Tells Your Care Team
The information displayed on the contraction monitor is an important tool for the healthcare team to assess the progress of labor and the overall condition of the birthing person and baby. By observing the frequency, duration, and pattern of contractions, providers can determine if labor is progressing effectively.
Monitoring also helps identify potential concerns, such as contractions that are too frequent or too long, which could affect blood flow to the placenta. This data, combined with other assessments, guides decisions about labor management, including whether interventions are needed. The monitor provides a continuous record of uterine activity, which aids in the comprehensive assessment of labor progression.