Fetal heart rate (FHR) is the speed and rhythm of a baby’s heartbeat in the womb. Monitoring FHR indicates fetal well-being throughout pregnancy and labor, offering insights into the baby’s health and response to its environment.
The Importance of Fetal Heart Rate Monitoring
Monitoring fetal heart rate is a component of prenatal care, offering insights into the baby’s health and development. It helps healthcare providers assess the baby’s oxygen supply and overall condition. Observing the heart rate aids in identifying potential complications, such as distress or insufficient oxygen, allowing for timely medical intervention. It also helps evaluate the baby’s status during labor, guiding decisions regarding interventions.
Clinical Methods for Measuring Fetal Heart Rate
Healthcare providers use various methods to measure fetal heart rate in clinical settings, each suited for different stages of pregnancy and labor. These techniques range from simple auscultation to complex electronic monitoring systems.
Auscultation
Auscultation involves listening to the fetal heartbeat using specialized handheld devices. A handheld Doppler device uses sound waves to detect the heartbeat. Healthcare providers commonly use Dopplers during routine prenatal visits. A fetoscope, similar to a stethoscope, can be pressed against the mother’s abdomen to listen. These methods are employed for intermittent checks throughout pregnancy and labor.
Ultrasound Scans
Routine prenatal ultrasound examinations detect fetal heart rate. A transvaginal ultrasound can detect cardiac tissue activity as early as 5.5 to 6 weeks gestation. By 6.5 to 7 weeks, the heartbeat can be better assessed. This early detection confirms a viable pregnancy and helps determine gestational age.
Non-Stress Test (NST)
A non-stress test measures fetal heart rate in response to fetal movement and uterine contractions. During this test, monitors are placed on the mother’s abdomen to record the baby’s heart rate and uterine activity. A normal response shows an increase in heart rate when the baby moves. This test is often performed in the third trimester, after 28 weeks, or for high-risk pregnancies.
Contraction Stress Test (CST) / Oxytocin Challenge Test (OCT)
The contraction stress test (CST), also known as the oxytocin challenge test, evaluates the baby’s heart rate response to uterine contractions. This test is performed when there are concerns about the baby’s health or if non-stress test results are unclear. During a CST, contractions are stimulated by nipple stimulation or by administering oxytocin intravenously. The test assesses whether the placenta can provide sufficient oxygen to the fetus during the temporary reduction in blood flow caused by contractions.
Continuous Electronic Fetal Monitoring (EFM)
Continuous electronic fetal monitoring (EFM) is used during labor to track the baby’s heart rate and the mother’s contractions. External EFM involves placing two sensors on the abdomen; one measures fetal heart rate, and the other records uterine contractions. Internal EFM, used when external monitoring is insufficient or precise readings are needed, involves attaching a thin wire electrode directly to the baby’s scalp. Another internal method uses an intrauterine pressure catheter to measure contraction strength.
Monitoring Fetal Heart Rate at Home
At-home fetal Doppler devices allow expectant parents to listen to their baby’s heartbeat. These handheld devices use sound waves to detect and amplify the fetal heartbeat. To use them, ultrasound gel is applied to the lower abdomen, and the probe is moved until the heartbeat is detected.
At-home fetal Dopplers have limitations and risks. They are not diagnostic tools and cannot assess the baby’s well-being or detect distress. They can provide false reassurance if a heartbeat is heard but other problems exist.
It is common to pick up other sounds, such as the mother’s own heartbeat, the umbilical cord, or intestinal movements, which can be mistaken for the baby’s heartbeat. The U.S. Food and Drug Administration (FDA) advises against their routine use. Home monitoring should never replace regular professional prenatal care, and any concerns about fetal movement or health should prompt immediate consultation with a healthcare provider.
Understanding Fetal Heart Rate Readings
A normal fetal heart rate typically ranges between 110 and 160 beats per minute (bpm) for most of pregnancy. This range can vary slightly depending on gestational age, starting around 90-110 bpm in early pregnancy and peaking around 140-170 bpm by week nine, before settling into the typical range. The fetal heart rate can fluctuate by 5 to 25 beats per minute as the baby responds to conditions in the uterus.
Variations in heart rate patterns, such as accelerations and decelerations, provide information about fetal health. Accelerations are temporary increases in the fetal heart rate, usually by at least 15 bpm for at least 15 seconds, and are associated with fetal movement. These are a reassuring sign. Decelerations are temporary decreases in the heart rate. Early decelerations, which mirror uterine contractions, are normal and often caused by head compression during labor. Late decelerations, where the heart rate drops after the peak of a contraction, and variable decelerations, which are abrupt and irregular drops, can indicate reduced oxygen supply or umbilical cord compression.
Contact a healthcare provider if there are changes in the baby’s movement or if home monitoring suggests consistently low or high heart rate readings. Medical professionals interpret fetal heart rate patterns and provide appropriate medical advice.