Contraction monitoring is a common practice during labor to observe uterine activity and assess fetal well-being. This process involves using specialized equipment that translates physical changes in the uterus into a visual representation. Understanding how contractions appear on this monitor can provide valuable insight into the progression of labor and the health of both the birthing person and the baby. The information displayed helps healthcare providers make informed decisions throughout the labor process.
Understanding the Monitoring Process
Contractions are monitored externally using a tocodynamometer, or toco. This transducer is placed on the abdomen, secured with a belt, over the area where contractions are felt most strongly. The toco measures changes in the uterine wall’s shape and tension as it contracts and relaxes. These physical changes convert into electrical signals, displayed as a graphical tracing on a screen or printed paper.
The external toco primarily measures the frequency and duration of contractions. It approximates intensity by sensing abdominal tightening but does not directly measure precise internal uterine pressure. An internal uterine pressure catheter (IUPC) is needed for precise intensity measurement, which is a more invasive method. The external monitor provides a continuous record for ongoing assessment of uterine activity.
Reading the Contraction Tracing
Contractions appear as wave-like patterns on the monitor. The tracing has a horizontal X-axis representing time, marked in minutes with smaller increments for seconds. The vertical Y-axis indicates the relative pressure or intensity of the contraction. For external monitoring, these units are arbitrary, not precise measurements like millimeters of mercury (mmHg).
Each individual contraction wave on the tracing has distinct parts. The “baseline” or “resting tone” is the flat line between contractions, indicating the uterus is relaxed. As a contraction begins, the line moves upward, called the “increment.” The highest point is the “acme” or “peak,” representing the strongest point.
Following the peak, the line descends, known as the “decrement,” as the contraction subsides. Duration is measured from the beginning of the increment to the end of the decrement, while frequency is the time from the start of one contraction to the start of the next.
What Different Patterns Indicate
Observing contraction patterns on the monitor provides significant information about labor progression. True labor contractions exhibit a regular pattern, becoming progressively more frequent, longer, and increasing in intensity, appearing as higher peaks. These contractions effectively cause cervical changes, such as effacement and dilation.
In contrast, Braxton Hicks contractions, often called “practice contractions” or “false labor,” appear irregular. They are less intense, showing lower peaks, and are shorter in duration compared to true labor. Unlike true labor, Braxton Hicks contractions do not lead to cervical changes and may subside with activity changes or hydration.
The monitor may show patterns indicating excessive uterine activity, referred to as hypertonus or tachysystole. Tachysystole is defined as more than five contractions within a 10-minute period, averaged over 30 minutes. These patterns include contractions lasting over two minutes or occurring too frequently with insufficient resting time. Such activity can reduce oxygen supply to the baby.
How Contraction Information Guides Care
Healthcare providers use contraction monitoring information to assess labor progress and effectiveness. By analyzing contraction frequency, duration, and approximate intensity, they determine if labor advances as expected. This assessment helps understand if contractions are sufficient to cause cervical dilation and effacement.
The monitor also helps identify potential concerns, such as contractions that are too strong, too frequent, or ineffective. For example, observing tachysystole may signal an overworking uterus, potentially affecting fetal well-being. This data guides interventions, including adjusting medications like oxytocin, changing maternal position, or preparing for delivery. Continuous monitoring provides essential insights for a safe labor and delivery.