What do those squiggly tracings mean to a laboring woman and her family? The sound of an unborn baby's heart galloping along in the hours before birth is a beautiful thing, but the machine also produces a tracing that's easy to use and understand.
Find the Baseline Fetal Heart Rate
This should be on average between 120 and 160 beats per minute. The baby's heart rate is traced on the top half of the monitor strip. Variability is normal; it should range within a ten beat span, so the baseline will be something like 120 to 130, or 134 to 144. This is the baby's normal (non-stressed) heart rate.
Determine the Length and Distance between Contractions
Monitors are typically set to either one or three minutes per inch. The toco is an external instrument strapped to the mother's abdomen that is sensitive to pressure. It traces contractions on the bottom of the monitor strip, beginning at a baseline of usually zero or ten and climbing gradually as the contraction peaks, then descending as it wanes. The toco tracing will indicate how long contractions last and how far apart they are. Without other instruments the monitor cannot measure the force of contractions. The height of contraction "hills" on monitor paper varies by the mother's size and the position of the toco. Coughing and bearing down will change the toco tracing.
The Tracing Can Help a Mother Respond to Labor
EFM will typically show the beginning of a contraction before the mother feels it, a feature that can be useful if the mother needs a "heads up" to take a deep cleansing breath before she is caught off-guard. Accordingly, the monitor may show the contraction has ended while the mother is still experiencing pain; watching the tracing will let her know when the uncomfortable pressure is almost over.
A mother under epidural anesthesia should still breathe slowly and deeply to oxygenate the fetus during contractions. The monitor can tell her when she is having a "pain" even though she doesn't feel it.
Watch for Correlations between Contractions and Heart Rate
As long as there is variability, it is fine if the baby's heart rate remains at baseline during labor. Possibly they are sleeping! A rise in the number of beats per minute at the start of contractions is reassuring; the placenta is functioning well and the baby is receiving enough oxygen. Variable decelerations are V shaped and can occur anytime there is cord compression; caregivers will ask the mother to change her position to remedy this concern. Late decelerations are dips below the baseline that occur at the end of contractions and take longer to return to baseline. These indicate the baby is under serious stress and has low oxygen stores. This situation should not be allowed to continue. The mother may be given oxygen, turned on her left side to improve circulation, and any IV medications used to stimulate contractions will be reduced or suspended. If the condition is not remedied, delivery by cesarean section may become necessary.
During pushing, however, decelerations are a normal response to head compression. The baby recovers quickly between contractions, which are naturally spaced further apart at this stage.of labor.
This article is not intended to replace professional training in the interpretation of electronic fetal monitor strips.
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