External and Internal Heart Rate Monitoring of the Fetus

By Nancy Bowers

(Fetal Monitoring, External and Internal)

Procedure Overview

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 or 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:

  • 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

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