Cardiotocography (CTG) is a widely used monitoring technique during pregnancy and labor. The term “cardio” refers to the baby’s heart, “toco” to uterine contractions, and “graphy” signifies recording. This non-invasive procedure tracks the baby’s heart rate and the mother’s uterine contractions, providing real-time information about fetal well-being as labor progresses.
The Purpose of Cardiotocography
Cardiotocography assesses the baby’s well-being and oxygen supply. By continuously monitoring the baby’s heart rate in relation to uterine contractions, healthcare providers gain insight into how the fetus is responding within the womb. Observing how the baby’s heart rate changes during and after a contraction can reveal signs that might suggest a need for closer attention. This assessment helps identify situations where the baby might be experiencing stress, guiding medical decisions to support fetal health.
The Monitoring Process
The most common method is external monitoring. Two elastic belts are placed around the mother’s abdomen: one with an ultrasound transducer to detect the baby’s heart rate, and the other with a pressure sensor to measure uterine contractions. This setup is generally painless and allows the mother to remain comfortable.
Internal monitoring is a less common alternative, typically reserved for active labor when a more precise reading is required. This method involves placing an electrode directly onto the baby’s scalp for accurate fetal heart rate measurement. An intrauterine pressure catheter (IUPC) may also be inserted into the uterus to measure contraction strength and timing directly.
Interpreting the Results
Interpreting a cardiotocography trace involves analyzing several distinct components that collectively indicate the baby’s condition. The top part of the CTG trace displays the baby’s heart rate, while the bottom section shows uterine contractions. Understanding these patterns helps healthcare providers assess fetal well-being.
Baseline Fetal Heart Rate
The baseline fetal heart rate represents the baby’s average heart rate between contractions, usually measured over a 10-minute period. A normal baseline heart rate for a baby during labor typically falls between 110 and 160 beats per minute (bpm). Variations outside this range, either persistently high (tachycardia) or low (bradycardia), may prompt further investigation.
Variability
Variability refers to the small, normal fluctuations in the fetal heart rate, which indicate a healthy and active nervous system. Normal variability is generally observed as oscillations between 5 and 25 bpm. Periods of reduced variability, less than 5 bpm, can occur normally when the baby is in a sleep cycle, which typically lasts up to 50 minutes. However, prolonged reduced variability may signal a need for closer assessment.
Accelerations
Accelerations are brief, temporary increases in the fetal heart rate, typically rising at least 15 bpm above the baseline and lasting 15 seconds or more. These increases often coincide with fetal movements and are considered reassuring signs of a well-oxygenated baby, indicating a healthy neurological response.
Decelerations
Decelerations are temporary decreases in the fetal heart rate, and their significance depends on their timing in relation to contractions. Early decelerations appear as a mirror image of the uterine contraction, beginning with the contraction’s onset and returning to the baseline by its end. These are generally considered benign and are often associated with head compression. Late decelerations begin after the peak of a contraction and return to baseline after the contraction has ended, potentially indicating reduced oxygen transfer to the baby. Variable decelerations are more irregular in their shape, depth, and timing relative to contractions, and are frequently associated with umbilical cord compression. The specific type and pattern of decelerations guide further clinical evaluation.
Contractions
The bottom half of the CTG trace displays contractions, showing their frequency, duration, and intensity. Analyzing this pattern alongside the fetal heart rate helps medical staff understand the baby’s response to uterine activity.
Actions Based on CTG Readings
When a cardiotocography reading is “non-reassuring,” it does not automatically mean the baby is in immediate danger. Instead, it signals that closer observation and potential intervention are warranted to ensure fetal well-being. Healthcare providers address any concerns promptly.
Medical staff often begin with simple interventions to improve the fetal heart rate pattern. These include changing the mother’s position to relieve umbilical cord pressure or improve uterine blood flow. Providing intravenous fluids can enhance placental perfusion. Administering oxygen to the mother is another common step to increase oxygen available to the baby. If these initial measures do not improve the CTG pattern, further assessment, such as a fetal scalp blood sample, or other interventions may be considered to ensure the baby’s safety and health.