The pattern of the fetal heart rate is monitored during labor, as one way to detect if the fetus is in distress.
Starting soon after a woman in labor is admitted to the hospital, the doctor or another health care professional monitors the fetus’s heartbeat either periodically or continuously. Monitoring the fetus’s heart rate is the easiest way to determine whether the fetus is receiving enough oxygen. Abnormalities in the heart rate (too fast or too slow) and variations in the heart rate (over time and in response to contractions) may indicate that the fetus is in distress (fetal distress).
Types of Fetal Heart Monitoring
The fetus’s heart rate can be monitored in the following ways:
Externally: A fetoscope (a type of stethoscope) or a handheld ultrasound device (which transmits and receives sound waves) can be placed on the woman's abdomen to monitor the fetal heart rate at regular intervals. Another type of ultrasound device can be placed on the woman’s abdomen to monitor the heart rate continuously. Devices that do continuous monitoring (called electronic fetal monitoring) typically also have a sensor that can detect and track contractions.
Internally: An electrode (a small round sensor attached to a wire) is inserted through the woman’s vagina and attached to the fetus’s scalp. The internal approach is typically used when there is a risk of problems during labor or when signals detected by the external device cannot be recorded. This approach can be used only after the membranes that contain the fetus have ruptured (described as "the water breaks").
When continuous electronic fetal monitoring begins during labor, often a nonstress test is done. A nonstress test evaluates the fetal heart rate for 20 to 40 minutes to check for specific patterns. Results are considered reactive (reassuring) or nonreactive (nonreassuring). If the result is nonreassuring, further assessment of the fetus's well-being is done, such as a biophysical profile.
For a biophysical profile, ultrasonography is used to produce images of the fetus in real time, and the fetus is observed for up to 30 minutes. Doctors evaluate the heart rate, amount of amniotic fluid, fetal breathing and movement, and assign a score of up to 10.
Based on the result of these tests, doctors may allow labor to continue or may do a cesarean delivery.
