Braxton Hicks contractions, often referred to as “practice contractions” or “false labor,” are a common physiological occurrence during pregnancy. These mild, sporadic tightenings of the uterine muscle are the body’s way of preparing for the work of labor without causing actual cervical change. When a pregnant individual presents for assessment, medical staff utilize external monitoring to assess uterine activity. Understanding how this monitoring equipment works and what the resulting data represents is important for interpreting these preparatory contractions.
How Uterine Activity is Measured During Monitoring
The primary tool for externally measuring uterine activity is the tocodynamometer, commonly called a “toco.” This device is a pressure-sensitive disc secured to the abdomen with an elastic belt, typically placed over the fundus, the top portion of the uterus. The toco works by sensing changes in the shape and tension of the maternal abdomen as the underlying uterine muscle contracts.
The monitor then translates this pressure change into a waveform on the printed strip or screen, providing data on the frequency and duration of the uterine tightening. The toco does not measure the actual strength of the contraction in millimeters of mercury (mmHg) inside the uterus. Instead, the reading is relative; factors like the mother’s body habitus, belt tightness, and sensor placement all influence the recorded amplitude. Clinicians must assess true contraction strength manually through palpation alongside the monitor reading.
How Braxton Hicks Appear on the Monitor
Braxton Hicks contractions are registered by the tocodynamometer because they represent a tightening of the uterine muscle that increases abdominal tension. On the monitoring strip, these events typically appear as irregular, low-amplitude hills or waves. They are usually characterized by a lower intensity reading, often registering in the range of 5 to 25 mmHg, which is significantly less than the pressure associated with active labor contractions.
The timing of these practice contractions is haphazard and non-rhythmic, lacking a predictable pattern of increasing frequency. Braxton Hicks contractions tend to be short in duration and often subside or disappear entirely if the patient changes position, walks around, or drinks water. Their overall irregular pattern and low, non-progressive amplitude distinguish them from the work of true labor.
Differentiating True Labor Patterns
The distinction between Braxton Hicks and true labor contractions is made through a clinical analysis of the overall pattern, not just the appearance of a single waveform. True labor contractions follow a predictable, progressive pattern, becoming longer, stronger, and closer together over time. On the monitor, these contractions exhibit a rhythmic regularity, with the frequency increasing and the duration consistently lasting between 30 and 70 seconds.
The intensity of true labor contractions will show a progressive rise in amplitude on the trace, often reaching an internal pressure of 40 to 60 mmHg during the active phase. Crucially, the uterus continues to contract despite changes in activity or hydration, unlike practice contractions that fade with movement. The monitor data—frequency, duration, and amplitude—must always be combined with a clinical assessment to confirm labor. A definitive diagnosis of true labor relies on observing progressive cervical dilation and effacement, which the external monitor cannot measure.
When Monitoring Indicates Concern
Regardless of how a contraction appears on the monitor, a patient should contact their healthcare provider when certain symptoms arise. Frequent contractions, even if they feel mild, warrant evaluation, especially if they occur four to six or more times within an hour before 37 weeks of gestation. The focus shifts from the intensity of the contraction to its persistent frequency in a preterm context.
Other immediate warning signs include a sudden gush or steady leak of fluid, which may signify a rupture of membranes. Any instance of vaginal bleeding or a significant decrease in the baby’s movement pattern also requires urgent medical attention. These symptoms necessitate a prompt clinical assessment to ensure the well-being of both the mother and the baby.