When the baby has difficulty getting oxygen, changes in the baby's heart rate alert the health-care professionals to take action to help correct the situation. Mothers in labor can be monitored both externally and internally. External monitoring is virtually painless and generally simple. To obtain the baby's heart rate and the mother's uterine contractions, two monitor leads are placed on the abdomen outside the uterus by straps. Lubricant may be placed on the abdomen where the baby's heart rate is heard to help pick up the sound.
Ultrasonic waves detect heart action and obtain the baby's heart rate.
A normal baby's heart rate tracing looks like a choppy, irregular line. An average baby's heart rate is 120 to 160 beats per minute. Physicians observe the tracings for accelerations and decelerations of the heart rate, which indicate how well the baby is responding to the stress of labor. The external uterine contraction lead detects contractions by a pressure button. The machine converts this pressure to a graphic display on the lower portion of the paper.