The labor and delivery monitor displays two main readings stacked on top of each other: your baby’s heart rate on top and your contractions on the bottom. Understanding what these numbers and patterns mean can make the experience of labor less intimidating, even though your medical team is the one interpreting them in real time. Here’s how to make sense of what you’re seeing on that screen and on the printed strip.
The Two Lines on the Monitor
Two sensors are placed on your abdomen during labor. One sits over the baby’s heart and tracks the fetal heart rate (FHR), displayed as the upper tracing on the screen. The other sensor sits near the top of your uterus and detects contractions, displayed as the lower tracing.
The upper number on the digital display shows the baby’s heart rate in beats per minute. A normal baseline ranges from 110 to 160 beats per minute. You’ll see this number change constantly, which is expected and actually a good sign (more on that below). The lower number reflects uterine activity. With external monitoring, this number doesn’t measure the exact strength of your contractions. It shows relative changes, so you’ll see the number climb during a contraction and fall back down between them. Only internal monitoring with a pressure catheter placed inside the uterus can measure true contraction strength in millimeters of mercury.
What the Baby’s Heart Rate Should Look Like
The top tracing should hover in that 110 to 160 range as a baseline. The line won’t be flat, though. A healthy baby’s heart rate fluctuates constantly, creating a jagged, squiggly line rather than a smooth one. These fluctuations are called variability, and they’re one of the most important things your care team watches.
Variability is graded by how much the heart rate bounces around:
- Moderate (6 to 25 beats of fluctuation): This is the ideal pattern. It means the baby’s nervous system is active and responding normally.
- Minimal (5 beats or less): The line looks almost flat. This can be normal if the baby is sleeping (babies cycle through sleep periods during labor), but it gets more attention if it lasts a long time.
- Absent (no visible fluctuation): The line is completely smooth. This is concerning and prompts immediate evaluation.
- Marked (more than 25 beats): Large, exaggerated swings. This is uncommon and also warrants closer monitoring.
If you glance at the monitor and the line looks like a messy zigzag within the normal range, that’s generally what everyone wants to see.
Accelerations: The Reassuring Spikes
You’ll occasionally see the baby’s heart rate jump up sharply for a brief period, creating a hill on the tracing. These upward spikes are called accelerations, and they’re a sign of a healthy, well-oxygenated baby. They often happen when the baby moves. If you feel a kick and then see the heart rate jump, that’s a classic acceleration. Your nurse may even note these approvingly. The more you see them, the more reassuring the overall picture.
Decelerations: Dips to Watch For
Decelerations are temporary drops in the baby’s heart rate. They show up as downward dips on the upper tracing. Not all decelerations are worrisome, but the type, timing, and pattern matter a lot.
Early Decelerations
These dips mirror contractions almost perfectly. The heart rate starts to drop as the contraction builds, reaches its lowest point right at the peak of the contraction, and recovers as the contraction fades. They look like a mirror image of the contraction curve below them. Early decelerations are caused by mild pressure on the baby’s head during contractions and are considered harmless. The baby’s oxygen levels remain normal throughout.
Variable Decelerations
These are sharp, sudden drops that don’t follow a predictable pattern with contractions. They can vary in shape, depth, and timing, which is how they got their name. They’re caused by temporary compression of the umbilical cord. Occasional variable decelerations are common and usually not a problem, but if they keep happening with every contraction or become deeper and longer, your team will pay close attention.
Late Decelerations
These are the most concerning type. The heart rate dip starts after the contraction has already peaked and doesn’t recover until well after the contraction ends. There’s a visible lag between the contraction and the deceleration. Late decelerations suggest the placenta isn’t delivering enough oxygen to the baby during contractions. A single late deceleration may not be alarming, but a repeating pattern of late decelerations, especially combined with minimal or absent variability, signals a serious problem that requires prompt action.
Reading the Contraction Tracing
The bottom line on the monitor tracks your uterine activity. During a contraction, you’ll see the line rise into a hill shape and then come back down. Between contractions, the line should return to a resting level. Three things matter about contractions: how often they come, how long they last, and how strong they are.
Frequency is measured from the start of one contraction to the start of the next. In early labor, contractions typically come every 10 to 15 minutes. As labor progresses, they get closer together. Duration is how long each contraction lasts from start to finish. Early contractions may last only 10 to 15 seconds, gradually lengthening to 40 to 45 seconds or more as labor advances.
With an external monitor (the belt on your belly), you can see the timing and pattern of contractions clearly, but the height of the peaks doesn’t reliably reflect how strong they actually are. The sensor picks up the tightening of your abdominal wall, so its readings can be affected by your body type, the position of the sensor, and how you’re lying. Your nurse may press on the top of your uterus during a contraction to manually gauge its firmness. If your care team needs precise pressure measurements, they may place an internal pressure catheter after your water has broken. This thin tube sits inside the uterus and gives exact readings in millimeters of mercury.
One pattern your team watches for is too many contractions too close together, defined as more than five contractions in a 10-minute window across two consecutive intervals. This can reduce the baby’s recovery time between contractions and sometimes requires medication to slow things down, particularly if labor-stimulating drugs are being used.
External vs. Internal Monitoring
Most people are monitored externally with the two belts strapped around the abdomen. This is noninvasive and works well in the majority of labors. Sometimes, though, the external sensors struggle to get a reliable signal. This can happen if the baby is in an unusual position, if you’re moving a lot, or if body composition makes it harder for the sensor to pick up the signal clearly.
In those situations, or if labor isn’t progressing as expected, your team may recommend internal monitors. A fetal scalp electrode is a tiny wire attached to the baby’s scalp that gives a more precise heart rate reading. An intrauterine pressure catheter is a thin tube placed alongside the baby that measures contraction strength directly. Both require your membranes (water) to be broken first. Internal monitors are not routine and are placed only when there’s a specific clinical reason, such as an inability to track the baby externally or concerns about labor progress.
Putting It All Together
When you look at the monitor, the picture your care team builds comes from combining several elements at once: Is the baseline heart rate in the normal range? Is there good variability (that reassuring zigzag)? Are there accelerations? Are there decelerations, and if so, what type? How are the contractions spaced, and does the baby recover well between them?
A reassuring tracing shows a baseline between 110 and 160, moderate variability, occasional accelerations, no late or significant variable decelerations, and contractions with adequate rest periods in between. The tracing your team worries about most is one showing absent variability combined with recurrent late decelerations, recurrent severe variable decelerations, or a very slow heart rate that doesn’t recover. This pattern indicates the baby isn’t tolerating labor well and triggers rapid intervention.
Most tracings fall somewhere in between these two extremes, and your nurse will reposition you, adjust fluids, or take other steps to optimize the pattern. If you’re watching the monitor and see numbers dip or spike briefly, that alone doesn’t mean something is wrong. The overall trend and the combination of features are what matter, not any single number at any single moment.