CTG Fetal Monitoring: How Your Baby's Heart Rate Is Tracked During Labor

What Is CTG and Why Is It Used During Labor?

CTG (cardiotocography) is a monitoring technology that continuously tracks your baby's heart rate and your uterine contractions during labor. It helps healthcare providers assess whether your baby is receiving enough oxygen and responding well to the stress of contractions, allowing early intervention if any concerns arise.

Cardiotocography, commonly known as CTG or electronic fetal monitoring (EFM), has become a standard part of maternity care in hospitals around the world. The name comes from the Greek words for heart (cardio), uterine contractions (toco), and recording (graphy). This technology provides your healthcare team with continuous, real-time information about how your baby is coping during the birthing process.

During labor, your uterus contracts powerfully to help push your baby down through the birth canal. Each contraction temporarily reduces blood flow through the placenta, which means your baby receives slightly less oxygen during each squeeze. A healthy baby can easily cope with these brief interruptions, and their heart rate responds in predictable ways. CTG monitoring allows healthcare providers to see exactly how your baby's heart is responding, providing reassurance when everything is normal and early warning if intervention might be needed.

The development of CTG technology in the 1960s represented a major advancement in maternity care, giving clinicians objective data about fetal wellbeing rather than relying solely on intermittent listening with a stethoscope. Today, CTG is used in approximately 85% of hospital births in developed countries, making it one of the most common medical procedures during childbirth.

It's important to understand that CTG is a monitoring tool, not a treatment. It provides information that helps your healthcare team make decisions about your care. In most cases, the CTG trace is reassuring, confirming that your baby is doing well. When concerns do arise, having continuous monitoring means problems can be identified early, before they become serious.

When is CTG monitoring used?

CTG monitoring may be recommended in various situations during labor. For low-risk pregnancies, intermittent monitoring (listening to your baby's heart rate at regular intervals) may be sufficient. However, continuous CTG is generally recommended in certain circumstances where closer monitoring is beneficial.

Continuous CTG monitoring is typically used when there are risk factors that increase the chance of complications during labor. These include induced labor, use of oxytocin to strengthen contractions, epidural anesthesia, previous cesarean section, high-risk pregnancies (such as preeclampsia, diabetes, or growth restriction), multiple pregnancies (twins or more), and any signs of concern during labor such as meconium-stained amniotic fluid or maternal fever.

Even in low-risk pregnancies, most hospitals will perform at least an initial CTG assessment when you arrive in labor to establish a baseline reading of your baby's heart rate pattern. This initial monitoring typically lasts 20-30 minutes and helps your healthcare team understand how your baby is doing at the start of labor.

How Does CTG Monitoring Work?

CTG uses two sensors placed on your abdomen: an ultrasound transducer that detects your baby's heart rate, and a pressure-sensitive device (tocodynamometer) that measures the timing of your contractions. The machine displays two continuous lines showing how your baby's heart responds to each contraction.

Understanding how CTG works can help you feel more comfortable and informed during your labor. The technology is remarkably straightforward, using the same basic ultrasound principles that create those images during your pregnancy scans. Here's a detailed look at the components and process.

The external sensors

The CTG machine uses two main sensors, both of which are placed on your abdomen and held in place with elastic belts. While these belts might feel somewhat cumbersome, they're designed to stay in place while still allowing you to move and change positions.

The first sensor is an ultrasound transducer that detects your baby's heart rate. This small, disk-shaped device emits high-frequency sound waves that bounce off your baby's moving heart and return to the sensor. By measuring these reflected waves, the device can calculate exactly how fast your baby's heart is beating, updated continuously. This is the same safe ultrasound technology used throughout pregnancy for scans and Doppler checks.

The second sensor is called a tocodynamometer (often just called a "toco"). This pressure-sensitive device sits on the top of your uterus (the fundus) and measures changes in abdominal pressure. When your uterus contracts, it becomes firmer and pushes outward slightly, which the sensor detects. While this sensor accurately shows when contractions occur, it can only estimate relative strength rather than measuring the actual pressure inside your uterus.

Some hospitals also use a small pulse oximeter on your finger during CTG monitoring. This measures your own heart rate, which helps ensure the machine is definitely tracking your baby's heartbeat rather than accidentally picking up yours. This is particularly useful if your heart rate is elevated during labor.

Setting up the monitoring

When your midwife or nurse sets up CTG monitoring, they'll first feel your abdomen to locate your baby's position. They'll then place the ultrasound sensor over the area where your baby's heart sounds are clearest and adjust it until they get a good, consistent signal. You'll usually hear your baby's heartbeat as a rhythmic whooshing sound from the machine.

The toco sensor is typically placed near the top of your uterus, where it can best detect the hardening of the uterine muscle during contractions. Once both sensors are in position and secured with belts, the machine will begin recording and displaying the two traces.

Finding the optimal sensor position sometimes requires adjustments, especially as you change position or as your baby moves. Your healthcare team may need to reposition the sensors occasionally throughout labor to maintain a good recording.

Internal monitoring options

In some situations, your healthcare team may recommend internal monitoring for more accurate readings. This is typically used when external monitoring isn't providing adequate information, particularly if the baby needs very close observation or if there are concerns about the external trace.

Internal fetal heart rate monitoring uses a small electrode that attaches to your baby's scalp. This scalp electrode provides a direct measurement of your baby's heartbeat, eliminating the signal issues that can sometimes occur with external monitoring. For this to be used, your membranes must have ruptured (waters broken) and your cervix must be at least partially dilated.

Internal contraction monitoring uses a thin, pressure-sensitive catheter that's inserted through your cervix into the uterus. Called an intrauterine pressure catheter (IUPC), this device measures the actual pressure inside your uterus during contractions. This is particularly useful when healthcare providers need to know exactly how strong your contractions are, such as when labor isn't progressing as expected.

How Do Doctors Read and Interpret CTG Results?

Healthcare providers analyze CTG traces by examining the baseline heart rate (normally 110-160 bpm), variability (healthy fluctuations of 5-25 bpm), accelerations (temporary increases with baby movement), and decelerations (temporary decreases, especially in relation to contractions). A normal trace shows all these features in healthy patterns.

Interpreting CTG traces requires specialized training and experience. Your midwife, nurse, and doctor continuously assess the monitoring throughout your labor, looking at several key features that together create a picture of how your baby is coping. Understanding these elements can help you follow along if your healthcare team discusses the trace with you.

Baseline fetal heart rate

The baseline heart rate is the average heart rate when your baby is "at rest" - not accelerating or decelerating. A normal baseline falls between 110 and 160 beats per minute. Most healthy babies have a baseline somewhere in the 120-150 range. Your healthcare team looks at the baseline over 10-minute periods to establish the overall pattern.

A baseline that's too high (tachycardia, above 160 bpm) or too low (bradycardia, below 110 bpm) can indicate various conditions and requires investigation. However, temporary changes in baseline are common and often normal - for instance, a baby may have a slightly higher heart rate if the mother has a fever or is dehydrated.

Variability

One of the most important features healthcare providers assess is variability - the small, beat-to-beat fluctuations in your baby's heart rate. A healthy baby's heart rate isn't steady like a metronome; it constantly varies by 5 to 25 beats per minute as the nervous system adjusts to moment-by-moment changes.

Good variability is one of the most reassuring signs on a CTG trace because it indicates your baby's brain and nervous system are working well. Reduced variability can occur normally when your baby is in a sleep cycle (typically lasting 20-40 minutes), but persistently reduced variability may indicate fetal compromise and warrants attention.

Accelerations

Accelerations are temporary increases in heart rate of at least 15 beats per minute lasting at least 15 seconds. These typically occur when your baby moves and are a very positive sign - they demonstrate that your baby's nervous system is responding normally to activity.

The presence of accelerations is highly reassuring and is one of the key features of a "reactive" or normal CTG trace. Most healthy babies will show at least two accelerations within a 20-minute period.

Decelerations

Decelerations are temporary decreases in your baby's heart rate. How these are interpreted depends greatly on when they occur in relation to your contractions and how quickly the heart rate recovers.

Early decelerations begin and end with contractions, caused by head compression as your baby descends through the birth canal. These are generally considered normal and physiological during active labor. Late decelerations begin after a contraction starts and continue after it ends. These can indicate reduced oxygen supply and are taken more seriously, especially if they persist. Variable decelerations are sudden drops that vary in timing relative to contractions. These are often caused by cord compression and are very common during labor. Most variable decelerations are benign, but certain patterns require attention.

What Happens If the CTG Shows Abnormal Results?

If CTG shows concerning patterns, your healthcare team will first try simple interventions: changing your position, giving fluids, reducing oxytocin if you're receiving it, or giving oxygen. They may take a small blood sample from your baby's scalp to check oxygen levels. If the baby remains distressed, delivery may be expedited via vacuum extraction or cesarean section.

Seeing concerning patterns on the CTG monitor can be alarming, but it's important to know that abnormal readings are common and often temporary. Your healthcare team is trained to respond appropriately, and most situations can be managed with simple interventions. Understanding what happens next can help reduce anxiety if you encounter this during your labor.

Initial responses to concerning CTG patterns

When the CTG shows patterns that concern your healthcare team, their first response is usually to try simple corrective measures. These interventions are designed to improve blood flow and oxygen delivery to your baby while the team assesses the situation.

Position changes are often the first intervention. Simply turning from your back onto your side, or trying hands-and-knees position, can relieve pressure on major blood vessels and the umbilical cord. Left lateral (left side) positioning is often recommended as it optimizes blood flow to the uterus and placenta.

If you're receiving oxytocin (syntocinon/pitocin) to stimulate contractions, your healthcare team may reduce or stop this medication. Sometimes contractions are coming too frequently, not allowing your baby enough recovery time between them. Reducing the contraction frequency often resolves CTG abnormalities.

Intravenous fluids may be given or increased to ensure you're well-hydrated, which supports good blood pressure and blood flow to the placenta. In some cases, supplemental oxygen may be provided, though evidence for its effectiveness is mixed.

Fetal blood sampling (scalp blood test)

If the CTG remains concerning despite initial interventions, your healthcare team may recommend taking a small blood sample from your baby's scalp. This test, called fetal blood sampling or scalp blood testing, measures the pH and lactate levels in your baby's blood, providing objective information about oxygen levels.

For this test, a small instrument is inserted through your cervix (which must be at least 3-4 cm dilated), and a tiny prick is made on your baby's scalp to collect a few drops of blood. The results are available within minutes and help your healthcare team decide whether labor can continue safely or whether delivery needs to be expedited.

Normal fetal blood pH is above 7.25, indicating good oxygen levels. A pH between 7.20 and 7.25 is borderline and usually leads to repeat testing in 30 minutes. A pH below 7.20 suggests your baby may not be getting enough oxygen and typically leads to a decision to deliver promptly.

When expedited delivery is needed

If your baby shows signs of significant distress that don't respond to interventions, or if fetal blood sampling indicates compromised oxygen levels, your healthcare team may recommend expedited delivery. The method depends on how dilated your cervix is and how urgent the situation is.

If your cervix is fully dilated and your baby has descended, instrumental delivery using vacuum (ventouse) or forceps may be the fastest option. These techniques help guide your baby out while you push, shortening the second stage of labor. If your cervix isn't fully dilated, or if the situation is very urgent, cesarean section may be necessary. In emergency situations, cesarean section can be performed very quickly to protect your baby.

It's worth noting that many babies who show concerning CTG patterns are born perfectly healthy. CTG is designed to be sensitive, meaning it will pick up potential problems even at the risk of occasional false alarms. Healthcare providers would rather investigate a concern that turns out to be nothing than miss a baby who needs help.

What Are the Benefits and Limitations of CTG?

CTG provides continuous, objective monitoring of fetal wellbeing and has been shown to reduce neonatal seizures. However, it has limitations including false positives that lead to unnecessary interventions, restricted mobility (unless wireless), and the need for skilled interpretation. Intermittent auscultation may be equally effective for low-risk labors.

Like any medical technology, CTG has both advantages and limitations. Understanding these can help you have informed conversations with your healthcare team about the most appropriate monitoring approach for your individual circumstances.

Benefits of CTG monitoring

CTG provides a continuous, objective record of your baby's heart rate pattern and your contraction pattern throughout labor. This creates documentation that can be reviewed if questions arise later and allows patterns to be identified that might be missed with intermittent listening.

Research has consistently shown that CTG monitoring reduces the rate of neonatal seizures, which are a marker of oxygen deprivation during birth. While this benefit is modest in absolute terms (reducing seizures by about 1 in every 660 monitored babies compared to intermittent listening), it represents a meaningful reduction in a serious complication.

CTG allows early detection of potential problems, giving healthcare teams time to intervene before a situation becomes critical. The continuous nature of monitoring means that changes in your baby's condition can be identified quickly, even while staff are caring for other patients.

For high-risk pregnancies and labors, CTG provides essential information that guides clinical decision-making. In situations where there's increased risk of fetal compromise, continuous monitoring offers reassurance or early warning that may be life-saving.

Limitations and considerations

CTG monitoring has a significant false-positive rate, meaning it sometimes indicates problems when the baby is actually doing well. This can lead to unnecessary interventions, including cesarean sections that wouldn't have been needed if a different monitoring approach had been used. Research suggests that compared to intermittent listening, CTG increases the cesarean section rate by about 60%, though the overall impact on outcomes for the baby (beyond seizure reduction) is minimal.

Traditional wired CTG systems can limit your mobility during labor, making it harder to move around, use the bath, or find comfortable positions. While wireless systems address this, they're not available everywhere. There's good evidence that being mobile and upright during labor can help labor progress and may reduce the need for interventions.

CTG interpretation requires skill and experience, and there can be significant variation in how different clinicians interpret the same trace. This subjectivity means that management decisions aren't always consistent. Various organizations have developed standardized interpretation guidelines to address this, but human variation remains.

For low-risk labors with no complications, intermittent auscultation (listening to your baby's heart rate at regular intervals with a handheld Doppler or Pinard stethoscope) may be equally effective at identifying problems while allowing greater freedom of movement. Many guidelines recommend offering this option to women having uncomplicated labors.

Can You Move Around During CTG Monitoring?

Yes, many hospitals now have wireless (telemetric) CTG systems that allow you to walk freely, use a birthing ball, shower, or even get in the bath while being monitored. With traditional wired systems, movement is more limited but you can still change positions in bed. Discuss your options with your midwife.

One of the historical drawbacks of CTG monitoring was that it tethered laboring women to the bed or at least to a small area near the monitoring equipment. This restricted the natural instinct to move during labor and potentially slowed labor progress. Fortunately, technology has evolved to address these concerns.

Wireless (telemetric) CTG systems

Many modern maternity units now use wireless CTG systems that transmit data from the sensors to the monitoring station via radio or Bluetooth technology. With these systems, you can move freely around the room, walk the corridors, use a birthing ball, or even get into a shower or bath while continuous monitoring continues.

The sensors in wireless systems are similar to traditional ones but are connected to a small portable transmitter rather than wires leading to a monitor. The transmitted data appears on screens at the nurses' station and in your room, allowing your healthcare team to observe the trace even when you're mobile.

If wireless monitoring is important to you, it's worth asking about availability when you tour your maternity unit or at your antenatal appointments. Not all hospitals have these systems, and availability may be limited even where they exist.

Moving with traditional wired CTG

Even with traditional wired systems, you're not completely confined to lying on your back. The cables usually have enough length to allow you to sit on the edge of the bed, use a birthing ball beside the bed, stand next to the monitor, or adopt various positions on the bed including all-fours, side-lying, or semi-recumbent.

Talk to your midwife about optimizing your comfort and mobility within the constraints of the monitoring system. They can help you find positions that keep the sensors working well while still allowing you to move and respond to your body's needs during labor.

Intermittent monitoring as an alternative

If you're having an uncomplicated, low-risk labor and would prefer greater mobility, ask about intermittent auscultation instead of continuous CTG. With this approach, your baby's heart rate is listened to at regular intervals (typically every 15-30 minutes in the first stage of labor and every 5 minutes in the second stage) using a handheld Doppler or Pinard stethoscope.

Intermittent monitoring allows complete freedom of movement between checks. Research suggests that for low-risk labors, outcomes are similar to continuous monitoring, though you would move to continuous CTG if any concerns arose. Discuss this option with your healthcare team based on your individual circumstances and preferences.

Can CTG Be Used During Pregnancy Before Labor?

Yes, CTG can be used during pregnancy to monitor your baby's wellbeing, often called a non-stress test (NST). It's commonly used in high-risk pregnancies or if there are concerns about fetal movement. Antenatal CTG assessments typically last 20-60 minutes and look for reassuring patterns indicating your baby is healthy.

While most people associate CTG with labor monitoring, it's also a valuable tool for assessing fetal wellbeing during pregnancy. When used before labor begins, it's often called a non-stress test (NST) or antenatal cardiotocography.

When is antenatal CTG used?

Antenatal CTG monitoring may be recommended if you have a high-risk pregnancy that requires closer surveillance of your baby's wellbeing. This includes conditions such as gestational diabetes, preeclampsia, or high blood pressure. It may also be used if your pregnancy has gone past your due date, if you've noticed reduced fetal movements, if your baby appears small for dates or has growth restriction, if you have a multiple pregnancy (twins or more), or if previous tests have shown any concerns.

In some countries and hospitals, antenatal CTG is done routinely in the final weeks of pregnancy, while in others it's reserved for specific indications. Your healthcare provider will advise on the appropriate monitoring schedule for your situation.

What happens during an antenatal CTG?

The procedure is similar to labor CTG - sensors are placed on your abdomen to record your baby's heart rate and any uterine activity (Braxton Hicks contractions are common in late pregnancy). You'll usually be seated in a comfortable chair or reclining position.

Antenatal CTG assessments typically last 20-60 minutes. Healthcare providers look for a reactive trace - one that shows a normal baseline heart rate with good variability and at least two accelerations (temporary increases in heart rate with fetal movement) within a 20-minute period. These features indicate that your baby's nervous system is working well and they're getting adequate oxygen.

If the initial trace isn't reactive, this doesn't necessarily mean there's a problem - your baby may simply be in a sleep cycle. You might be given something cold to drink or asked to move around to stimulate your baby, and monitoring may continue for longer. Most non-reactive traces become reactive with time or stimulation.

CTG during external cephalic version

CTG monitoring is also used during external cephalic version (ECV) - the procedure where a doctor manually turns a breech baby to head-down position. Continuous monitoring before, during, and after the procedure ensures your baby tolerates the turning well. If the CTG shows any concerning patterns during ECV, the procedure would be stopped immediately.

What Will CTG Feel Like During Labor?

CTG monitoring itself is painless. You'll feel the elastic belts holding the sensors in place on your abdomen, which some women find slightly uncomfortable or restrictive. The sensors may need occasional repositioning. You'll hear your baby's heartbeat as a rhythmic sound from the machine, which many parents find reassuring.

If you're wondering what to expect from CTG monitoring during your labor, it helps to know that the procedure itself causes no discomfort to you or your baby. The main things you'll notice are related to wearing the sensors and the sounds and displays of the machine.

Wearing the sensors

The elastic belts that hold the sensors can feel somewhat tight or cumbersome, especially as labor progresses and you want to move more freely. If the belts are uncomfortable, don't hesitate to ask your midwife to adjust them - they should be firm enough to keep the sensors in place but not so tight as to be painful.

The sensors themselves sit against your skin and are usually coated with a conductive gel to improve the signal. This gel is water-based and washes off easily. The ultrasound sensor for your baby's heart rate may feel slightly cold at first application.

You may find that the sensors slip out of position as you move, especially during strong contractions. Your healthcare team will check and reposition them as needed. Sometimes finding and maintaining a good signal can take a few attempts, particularly if your baby is in an unusual position or is very active.

What you'll see and hear

The CTG machine produces a continuous printout or digital display showing two lines. The upper line represents your baby's heart rate, fluctuating as the heart speeds up and slows down. The lower line shows your contractions, rising and falling like hills as your uterus tightens and relaxes.

Most CTG machines produce an audible representation of your baby's heartbeat - a rhythmic whooshing or beeping sound. Many parents find this sound reassuring, though it can become part of the background noise during a long labor. You can usually ask for the volume to be turned down if you prefer.

Numbers on the display show the current heart rate in beats per minute. Seeing this number fluctuate is completely normal - remember, variability in heart rate is actually a reassuring sign. Try not to become too focused on watching the numbers, as this can increase anxiety. Trust your healthcare team to interpret the trace and alert you if there are any concerns.

Impact on your birth experience

While CTG monitoring is an important safety measure, it's also one of many elements that shape your birth experience. Discuss with your healthcare team how to integrate monitoring with your birth preferences. Even with continuous monitoring, you can usually dim lights for a calmer environment, play music if you wish, have your partner close by, and use various comfort measures like massage or breathing techniques.

If you feel that the monitoring is becoming a source of stress or distraction, talk to your midwife. They can help reposition screens so you're not constantly watching them, adjust volumes to reduce auditory distraction, and provide reassurance about what the trace is showing.