External and Internal Heart Rate Monitoring of the Fetus
(Fetal Monitoring, External and Internal)
What is external and internal fetal heart rate monitoring?
Fetal heart rate monitoring is a procedure used to evaluate the well-being of the fetus by assessing the rate and rhythm of the fetal heartbeat.
During late pregnancy and labor, your physician/midwife may recommend monitoring the fetal heart rate and other functions. The average fetal heart rate is between 110 and 160 beats per minute, and can vary five to 25 beats per minute. The fetal heart rate may change as the fetus responds to conditions in the uterus. An abnormal fetal heart rate or pattern may indicate that the fetus is not getting enough oxygen or that there are other problems.
There are two methods for fetal heart rate monitoring, external and internal:
- External fetal heart rate monitoring uses a device to listen to or record the fetal heartbeat through the mother’s abdomen. A fetoscope (a type of stethoscope) is the most basic type of external monitor. Another type of monitor is a hand-held electronic Doppler ultrasound device. These methods are often used during prenatal visits to count the fetal heart rate. A fetoscope or Doppler device may also be used to check the fetal heart rate at regular intervals during labor.
Continuous electronic fetal heart monitoring may be used during labor and birth. An ultrasound transducer placed on the mother’s abdomen conducts the sounds of the fetal heart to a computer. The rate and pattern of the fetal heart are displayed on the computer screen and printed onto special graph paper.
- Internal fetal heart rate monitoring uses an electronic transducer connected directly to the fetal skin. A wire electrode is attached to the fetal scalp or other body part through the cervical opening and is connected to the monitor. This type of electrode is sometimes called a spiral or scalp electrode. Internal monitoring provides a more accurate and consistent transmission of the fetal heart rate than external monitoring because factors such as movement do not affect it. Internal monitoring may be used when external monitoring of the fetal heart rate is inadequate, or closer surveillance is needed.
During labor, uterine contractions are usually monitored along with the fetal heart rate. A pressure-sensitive device called a tocodynamometer is placed on the mother’s abdomen over the area of strongest contractions to measure the length, frequency, and strength of uterine contractions. Because the fetal heart rate and uterine contractions are recorded at the same time, these results can be examined together and compared.
Internal uterine pressure monitoring is sometimes used along with internal fetal heart rate monitoring. A fluid-filled catheter is placed through the cervical opening into the uterus beside the fetus and transmits uterine pressure readings to the monitor.
Other procedures that may be used to monitor the well-being of the fetus include amniocentesis and chorionic villus sampling. Please see these procedures for additional information.
Anatomy of the fetus:
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- Amniotic sac - a thin-walled sac that surrounds the fetus during pregnancy. The sac is filled with amniotic fluid (liquid made by the fetus) and the amnion (the membrane that covers the fetal side of the placenta), which protects the fetus from injury and helps to regulate the temperature of the fetus.
- Anus - the opening at the end of the anal canal
- Cervix - the lower part of the uterus that projects into the vagina. Made up of mostly fibrous tissue and muscle, the cervix is circular in shape.
- Fetus - an unborn baby from the eighth week after fertilization until birth
- Placenta - an organ, shaped like a flat cake, that only grows during pregnancy and provides a metabolic interchange between the fetus and mother. (The fetus takes in oxygen, food, and other substances and eliminates carbon dioxide and other wastes.)
- Umbilical cord - a rope-like cord connecting the fetus to the placenta. The umbilical cord contains two arteries and a vein, which carry oxygen and nutrients to the fetus and waste products away from the fetus.
- Uterine wall - the wall of the uterus
- Uterus (Also called the womb.) - the uterus is a hollow, pear-shaped organ located in a woman's lower abdomen, between the bladder and the rectum, that sheds its lining each month during menstruation and in which a fertilized egg (ovum) becomes implanted and the fetus develops
- Vagina - the part of the female genitals, behind the bladder and in front of the rectum, that forms a canal extending from the uterus to the vulva
Fetal heart rate monitoring is used in nearly every pregnancy to assess fetal well-being and identify any changes that might be associated with problems during pregnancy or labor. Fetal heart rate monitoring is especially helpful for high-risk pregnancy conditions such as diabetes, high blood pressure, and problems with fetal growth.
Situations during pregnancy in which fetal heart rate monitoring may be used include, but are not limited to, assessment of fetal heart rate during prenatal physician visits and monitoring the effect of preterm labor medications on the fetus.
Fetal heart rate monitoring may be used as a component of other procedures, including, but not limited to, the following:
- Nonstress test (a procedure that measures the fetal heart rate in response to fetal movements)
- A contraction stress test (a procedure in which the fetal heart rate is observed with uterine contractions which have been stimulated with medication or other methods)
- A biophysical profile, or BPP (a test that combines a nonstress test with ultrasound)
Situations during labor which may affect the fetal heart rate and for which fetal heart rate monitoring may be used include, but are not limited to, the following:
- Uterine contractions
- Pain medications and/or anesthetic agents given to the mother during labor
- Procedures performed during labor
- Pushing during the second stage of labor
There may be other reasons for your physician to recommend fetal heart rate monitoring.
There is no radiation used and generally no discomfort from the application of the transducer to the abdominal skin.
The elastic belts that hold the ultrasound and pressure transducers in place around your abdomen may be slightly uncomfortable. These can be readjusted to help you feel more comfortable.
You must lie still during some types of fetal heart rate monitoring. You may be required to stay in bed during labor.
With internal monitoring, you may experience some slight discomfort during the insertion of the electrode.
Risks of internal monitoring include, but are not limited to, infection and bruising of the fetal scalp or other body part.
Internal fetal heart rate monitoring is contraindicated in women with active herpes lesions on the cervix or vagina because of the risk of transferring the infection to the fetus.
There may be other risks depending upon your specific medical condition. Be sure to discuss any concerns with your physician/midwife prior to the procedure.
Certain factors or conditions may interfere with the results of the procedure. These include, but are not limited to, the following:
- Obesity of the mother
- Position of the fetus or mother
- Too much amniotic fluid (polyhydramnios)
- Cervix not adequately dilated or amniotic sac not broken (for internal monitoring)
- Your physician/midwife will explain the procedure to you and offer you the opportunity to ask any questions that you might have about the procedure.
- You may be asked to sign a consent form that gives your permission to do the procedure. Read the form carefully and ask questions if something is not clear. The consent form for fetal heart rate monitoring may be included as part of the general consent for your labor and birth.
- If fetal heart rate monitoring is performed in conjunction with another monitoring procedure, such as a nonstress test or biophysical profile, you may be asked to eat a meal before the procedure. This can help increase fetal activity. You may or may not be able to eat or drink with fetal heart rate monitoring during labor.
- Although the gel applied to the skin during the procedure does not stain clothing, you may wish to wear older clothing or a hospital gown, as the gel may not be completely removed from your skin afterwards.
- Placement of an internal electrode requires that the amniotic membranes (the fluid- filled sac that surrounds the fetus during pregnancy) be broken, and the cervix be dilated (opened) several centimeters to allow contact with the fetal scalp or other body part.
- Based upon your medical condition, your physician may request other specific preparation.
Fetal heart rate monitoring may be performed in your physician’s office, on an outpatient basis, or as part of your stay in a hospital. Procedures may vary depending on your condition and your hospital’s practices.
Generally, fetal heart rate monitoring follows this process:
For external fetal heart rate monitoring:
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- Depending on the type of procedure, you may be asked to expose your abdomen, undress from the waist down, or undress completely and put on a hospital gown.
- You will lie on your back on an examination table.
- A clear gel will be applied to your abdomen (the gel acts as a conductor).
- The transducer will be pressed against the skin and moved around until the fetal heartbeat is located. You will be able to hear the sound of the fetal heart rate with Doppler or an electronic monitor.
- During labor, the fetal heart rate may be monitored intermittently or continuously, depending on your condition and the condition of your fetus.
- For continuous electronic monitoring, the transducer will be connected to the monitor with a cable. A wide elastic belt will be placed around your back to secure the transducer in place.
- The fetal heart rate will be recorded in the medical record. With continuous electronic monitoring, the fetal heart pattern will be displayed on a computer screen and printed onto graph paper.
- You may or may not be allowed to get out of bed with continuous external fetal heart rate monitoring.
- Once the procedure has been completed, the transducer will be removed and the gel will be wiped off.
For internal fetal heart rate monitoring:
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- You will be asked to undress completely and put on a hospital gown, and lie on a labor bed, with your feet and legs supported as for a pelvic exam.
- The physician/midwife or nurse will perform a vaginal examination with a gloved hand to check cervical dilation (the amount the cervix has opened). This may be slightly uncomfortable.
- If the amniotic sac is still intact, your physician/midwife may break open the membranes with an instrument. You will feel warm fluid coming out of your vagina.
- The physician/midwife will feel the part of the fetus at the cervical opening with gloved fingers - this is usually the head of the fetus.
- A long, plastic electrode guide will be inserted into your vagina. A small spiral wire at the end of the electrode will be placed against the fetal part and gently rotated into the fetal skin.
- The guide will be removed and the electrode will be left in place, attached to the fetal part.
- The electrode wires will be connected to the monitor cable and secured with a band around your thigh.
- You may or may not be allowed to get out of bed with continuous internal fetal heart rate monitoring.
- Once the baby is born, the electrode will be removed.
There is no special type of care required after external fetal heart rate monitoring. You may resume your normal diet and activity unless your physician/midwife advises you differently.
After internal fetal heart rate monitoring, the electrode site on the newborn baby will be examined for infection, bruising, or a laceration. The site may be cleansed with an antiseptic.
Your physician/midwife may give you additional or alternate instructions after the procedure, depending on your particular situation.