When monitoring a pregnancy, particularly during labor and delivery, medical staff rely on specialized equipment to track the well-being of both the expectant parent and the baby. This process, known as fetal monitoring, involves placing sensors on the abdomen to continuously record important physiological data. The monitor screen or paper printout displays various measurements and abbreviations that can look confusing to an untrained eye. One of the primary readings displayed alongside the baby’s heart rate is often labeled with the abbreviation “UA.”
Defining Uterine Activity
The abbreviation “UA” stands for Uterine Activity, representing the measurement of contractions. A contraction is the tightening and relaxing of the uterine muscle, which works to push the baby toward delivery. Monitoring this activity is important for assessing the progression of labor.
Tracking uterine activity helps the medical team gauge the strength and pattern of the labor process. This information provides insight into how the uterus is functioning and whether contractions are effective enough to advance labor. It is also used to assess the stress placed on the fetus and determine if interventions, such as adjusting medication or changing the parent’s position, are necessary.
Methods for Measuring Contractions
There are two primary methods medical professionals use to measure Uterine Activity, each offering different levels of detail.
External Monitoring
The most common method is External Monitoring, which uses a device called a tocodynamometer, often referred to as a “toco.” The toco is a pressure sensor placed on the abdomen and held in place with an elastic belt. It detects the change in abdominal shape when the uterus contracts.
The toco measures the frequency and duration of contractions, but it does not accurately measure the true intensity or strength. The external tracing is influenced by factors such as adipose tissue, the parent’s position, and the placement of the belt. Therefore, medical staff often manually palpate the abdomen to estimate the contraction’s actual strength.
Internal Monitoring
The second method is Internal Monitoring, which uses an Intrauterine Pressure Catheter (IUPC). This method is only possible after the amniotic sac has ruptured and involves inserting a thin tube into the uterus. The IUPC is considered the gold standard because it directly measures the pressure within the uterine cavity in millimeters of mercury (mmHg).
The IUPC provides the most accurate data for contraction intensity, along with frequency and duration. This internal method is reserved for situations where the external monitor is unreliable, such as with a higher body mass index. It is also used when there is a need to precisely calculate the force of the contractions to determine if labor is progressing adequately.
Interpreting Uterine Activity Data
Medical staff focus on three specific parameters when interpreting the UA tracing to understand the nature of the contractions.
Frequency
Frequency is the measurement of how often contractions occur, counted from the start of one contraction to the start of the next. Normal labor typically involves no more than five contractions in a 10-minute period, averaged over a 30-minute window.
Duration
Duration measures the length of time from the beginning of one contraction to the end of that same contraction. Contractions often last between 30 seconds and a minute during the active phase of labor.
Resting Tone
The Resting Tone is the pressure of the uterus between contractions. This is important because it signifies the recovery period for the fetus, allowing adequate blood flow and oxygen supply to return to the placenta. The average resting tone during labor is usually around 10 mmHg when measured internally. Medical professionals analyze the UA data alongside the Fetal Heart Rate (FHR) tracing to determine the overall well-being of the baby.