Fetal Heart Monitoring
Labor puts stress on both you and the baby. Fetal heart monitoring provides a way to make sure that the baby is handling the stress. Monitoring can be done through several techniques.
Electronic fetal heart monitoring uses either two belts or a wide, elastic band placed around the abdomen. A device attached to the belt or under the band uses an ultrasound-Doppler technique to pick up the fetal heartbeat. A second device uses a gauge to pick up the contractions.
An external contraction monitor can show the frequency and duration of contractions, but it can’t provide information about how strong they are. An external fetal heart monitor gives information about the fetus’s response to contractions and records variability — that is, periodic changes in heart rate that help to determine how the baby is tolerating the labor process.
You may hear your practitioner use the following terms to describe the fetal heartbeat:
Normal baseline heart rate: About 110 to 160 beats per minute.
Bradycardia: A decrease in the fetal heart rate from baseline to below 110 beats per minute that lasts for more than ten minutes.
Tachycardia: An increase in the fetal heart rate to above 160 beats per minute for more than ten minutes.
Accelerations: Brief increases above baseline in the fetal heart rate, often after a fetal movement. Accelerations are a reassuring sign.
Decelerations: These are intermittent decreases below the baseline fetal heart rate. The significance of decelerations depends on their frequency, how far the heart rate drops, and when they occur in relation to contractions. Decelerations are classified as early, variable, or late, according to when they occur in relation to contractions.
There tends to be a large variability in the interpretation of fetal heart rate tracings. For this reason, recently the National Institute of Child Health and Human Development created a new three-tier system for the interpretation of fetal heart rate tracings:
Category 1: Normal tracing — predicting normal fetal acid-base status
Category 2: Indeterminate tracing — requires closer observation and possible treatment (fluids, oxygen, change in position, and so forth)
Category 3: Abnormal tracing — predicting abnormal fetal acid-base status at the moment
Your practitioner uses an internal fetal heart monitor when your baby needs closer observation than is possible with external monitoring. Your practitioner may be concerned about how your baby is tolerating labor, or he may simply be having difficulty picking up the heart rate externally — if, for example, you’re having more than one baby.
The monitor is placed during an internal exam. It’s passed through the cervix via a flexible plastic tube. This procedure is no more uncomfortable than a pelvic exam. The tiny electrode is then attached to the baby’s scalp.
An internal monitor for contractions (called an internal pressure transducer, or IPT) is sometimes used to better assess how strong the contractions are. The monitor consists of thin, flexible, fluid-filled tubing, which is inserted between the fetal head and the uterine wall during an internal exam.
Sometimes, this same device is used to infuse saline into the uterus — if very little amniotic fluid is present or if the fetal heart tracing indicates the umbilical cord is being compressed.