Uterine contractions are the rhythmic tightening and relaxing of the uterine muscles, a fundamental process during labor. These contractions, also called surges, serve a dual purpose during childbirth: they help to progressively open and thin the cervix and to move the fetus down the birth canal. Monitoring these contractions is important to track labor progression and assess the well-being of both the birthing parent and the baby.
Measuring Contractions at Home
Individuals can assess uterine contractions at home by observing and tracking three characteristics: frequency, duration, and intensity. To measure frequency, note the time from the beginning of one contraction to the beginning of the next. Duration is measured from the moment a contraction starts until it completely ends. Recording these times, typically in seconds for duration and minutes for frequency, helps identify developing patterns.
Monitoring intensity subjectively involves placing a hand on the abdomen during a contraction. During a contraction, the uterus will feel hard, and it will soften as the contraction subsides. Contractions are often described as mild if the uterus feels soft, moderate if it feels firm but can be indented, and strong if it feels very firm and cannot be indented. True labor contractions become progressively stronger, longer, and more frequent over time, unlike Braxton Hicks or “practice” contractions which are irregular and do not intensify.
Keeping a written log of these details can provide information for healthcare providers. It is advised to contact a healthcare provider when contractions last about 45 to 60 seconds and occur every 5 minutes for at least an hour, especially if talking or walking becomes difficult during them. This information helps determine if it is time to go to the hospital or birthing center.
Medical Methods for Measuring Contractions
Healthcare professionals employ objective methods to measure contractions, offering more precise data than at-home assessments. External monitoring, known as tocodynamometry, uses a device called a tocodynamometer (toco) placed on the abdomen. This non-invasive sensor detects changes in abdominal tension caused by uterine contractions, providing information about their frequency and duration. However, a toco cannot accurately measure the true intensity of contractions or the resting tone of the uterus, as its readings can be influenced by factors such as maternal body habitus, position, and the monitor’s placement. It is commonly used for routine monitoring during labor and allows for some patient movement.
For more precise measurements, particularly when external monitoring is insufficient or labor progression is a concern, internal monitoring with an Intrauterine Pressure Catheter (IUPC) may be used. An IUPC is a thin catheter inserted into the amniotic space within the uterus, after the amniotic membranes have ruptured. This invasive method directly measures the pressure inside the uterus in millimeters of mercury (mmHg), providing accurate data on the frequency, duration, and true intensity of contractions. IUPCs are particularly useful in situations like stalled labor, during labor induction, or when assessing the adequacy of contractions, for example, by calculating Montevideo units (MVUs). While offering superior accuracy, internal monitoring carries a slight risk of infection or injury and is not used routinely.
Understanding Contraction Measurements
The measured parameters of contractions—frequency, duration, and intensity—provide insights into the progression of labor. As labor progresses, contractions become more frequent, moving from every 5 to 20 minutes in early labor to every 2 to 5 minutes in active labor.
In early labor, contractions might last 30 to 45 seconds, gradually increasing to 40 to 70 seconds in active labor. Longer durations suggest more effective uterine activity in dilating the cervix and moving the baby.
Increasing intensity signifies that contractions are becoming more powerful, which is necessary for the cervix to thin and open. For instance, an IUPC might show contractions reaching 40-60 mmHg during active labor. Healthcare providers use these measurements to assess the stage of labor, determine if labor is progressing effectively, and make informed decisions about potential interventions, such as adjusting labor-inducing medications.