The external tocodynamometer measures uterine contractions by detecting changes in what?

The external tocodynamometer is a device used during labor to monitor uterine contractions. It measures changes in abdominal wall contour, specifically the tightness and relaxation of the uterine muscles during contractions. As the uterus contracts, it pushes against the abdominal wall, which the tocodynamometer detects as changes in pressure. This allows healthcare providers to visualize the frequency and duration of contractions, which are critical for monitoring labor progress and ensuring the well-being of both the mother and the fetus.

Other options, such as fetal heart rate, maternal blood pressure, and uterine position, are not what the tocodynamometer specifically measures. While fetal heart rate monitoring is important for assessing fetal well-being, it involves a different type of sensor. Maternal blood pressure is also crucial during labor but is typically monitored separately. Uterine position, while relevant in understanding the overall labor progress, does not directly correlate to contraction monitoring performed by the tocodynamometer. Thus, abdominal wall contour is the correct answer, as it directly relates to how the tocodynamometer functions in measuring contractions.