A fetal monitor produces a paper strip (or digital screen) with two stacked graphs running continuously from left to right. The top graph tracks the baby’s heart rate in beats per minute. The bottom graph tracks uterine contractions. Learning to read these two graphs together gives you a real-time picture of how the baby is tolerating labor.
The Two Graphs on Every Strip
The top graph displays the fetal heart rate (FHR). The vertical scale runs from about 30 to 240 beats per minute, with most of the action happening between 110 and 160 bpm. Each small square on the horizontal axis represents a set interval of time, so as the paper scrolls, you’re watching the heart rate unfold minute by minute.
The bottom graph displays uterine activity. When contractions occur, you’ll see hill-shaped rises on this tracing. The vertical scale is measured in millimeters of mercury when an internal pressure sensor is used, though with the more common external belt monitor, the numbers on this axis don’t reflect true pressure. What matters on the bottom graph is the pattern: how often the hills appear, how long each one lasts, and how the baby’s heart rate on the top graph responds to them.
What a Normal Baseline Looks Like
The baseline is the average heart rate the baby maintains between contractions, when the tracing is relatively flat. A normal baseline falls between 110 and 160 bpm. A rate consistently above 160 is called tachycardia, and a rate below 110 is called bradycardia. Both can have benign explanations (a mother’s fever can push the baby’s heart rate up, for instance), but both also warrant attention from the care team.
A healthy baseline isn’t a perfectly straight line. It should have a slight jaggedness to it, like a pencil line drawn by a slightly shaky hand. This jaggedness is called variability, and it’s one of the most important things on the entire strip.
Why Variability Matters
Variability reflects the baby’s nervous system making constant, tiny adjustments to the heart rate. It’s measured by looking at the difference between the small peaks and troughs in the baseline, measured in beats per minute.
- Moderate variability (6 to 25 bpm fluctuation): This is the normal, reassuring pattern. The tracing looks slightly zigzagged.
- Minimal variability (less than 5 bpm): The tracing looks almost flat. This can happen when the baby is sleeping (typically lasting 20 to 40 minutes) or after the mother receives certain pain medications. Persistent minimal variability without an obvious cause is concerning.
- Absent variability: The line is completely smooth with no detectable fluctuation. This is the most worrisome pattern.
- Marked variability (greater than 25 bpm): The tracing looks wildly jagged. This is uncommon and needs evaluation.
Moderate variability is the single most reassuring feature on a fetal monitor strip. If you see that healthy zigzag pattern, the baby’s brain and heart are communicating well.
Accelerations: The Reassuring Spikes
Accelerations are temporary jumps in heart rate above the baseline. They look like upward bumps on the top graph. For a baby at 32 weeks or beyond, an acceleration is defined as a rise of at least 15 bpm above baseline, lasting at least 15 seconds but less than 2 minutes. Nurses sometimes call this the “15 by 15” rule.
Accelerations usually happen when the baby moves, stretches, or responds to stimulation. They’re a sign of a healthy, well-oxygenated baby. A “reactive” tracing, which is the goal of a non-stress test, means the strip shows at least two accelerations within a 20-minute window.
Decelerations: Dips Below the Baseline
Decelerations are temporary drops in heart rate. They appear as downward dips on the top graph. Not all decelerations are dangerous, but identifying which type you’re seeing is critical. There are three main patterns, and each one points to a different cause.
Early Decelerations
These dips start at the same time the contraction begins on the bottom graph and return to baseline by the time the contraction ends. The shape of the dip mirrors the shape of the contraction almost perfectly, like a reflection. Early decelerations are caused by the baby’s head being compressed during contractions, which triggers a reflex that temporarily slows the heart. They are generally considered harmless and are common during active labor as the baby moves through the birth canal.
Late Decelerations
Late decelerations look similar in shape to early decelerations (gradual, smooth, symmetric), but they’re shifted to the right on the strip. The dip begins at or after the peak of the contraction and doesn’t return to baseline until after the contraction has ended. This delay is the key feature. Late decelerations suggest the placenta isn’t delivering enough oxygen to the baby during contractions. They’re associated with placental insufficiency and are always taken seriously, especially when they recur with multiple contractions.
Variable Decelerations
Variable decelerations are the most common type and the easiest to recognize because they look different from the others. Instead of a smooth, gradual dip, they drop suddenly and sharply, forming shapes that resemble the letters U, V, or W. They vary in depth, duration, and timing relative to contractions, which is where the name comes from. Variable decelerations are caused by compression of the umbilical cord. Occasional, brief variable decelerations are common and not necessarily alarming, but deep or prolonged ones need prompt attention.
The VEAL CHOP Memory Trick
Many nurses and students use the mnemonic VEAL CHOP to remember what causes each pattern. Each letter in VEAL matches to a letter in CHOP:
- Variable decelerations → Cord compression
- Early decelerations → Head compression
- Accelerations → Okay (oxygen is good)
- Late decelerations → Placental insufficiency
This pairing makes the patterns easier to recall in real time. If you see a sharp, sudden dip, think cord. If you see a gentle mirror of the contraction, think head. If the dip comes late, think placenta. If you see a spike upward, the baby is doing fine.
Reading the Contraction Pattern
The bottom graph tells you about the timing and duration of contractions. Frequency is measured from the start of one contraction to the start of the next. Duration is measured from when a single contraction begins rising to when it returns to the resting level. During active labor, contractions typically come every 2 to 5 minutes and last 45 to 90 seconds each.
One pattern to be aware of is tachysystole, defined as six or more contractions within a 10-minute window. This pace doesn’t give the uterus (or the baby) enough recovery time between squeezes. Research has found that six or more contractions in 10 minutes is significantly associated with fetal heart rate decelerations, which makes sense: the placenta needs those rest periods to restore blood flow and oxygen to the baby.
External Versus Internal Monitoring
Most fetal monitoring is done externally with two sensors held against the mother’s abdomen by elastic belts. One sensor uses ultrasound to detect the baby’s heartbeat, and the other uses a pressure-sensitive disc to detect contractions. This setup is noninvasive and works well for most labors.
Internal monitoring involves a tiny electrode placed on the baby’s scalp after the membranes have ruptured. It gives a more direct electrical reading of the heart rate. However, comparative studies have found the average difference between external abdominal sensors and internal scalp electrodes is only about 0.35 bpm, making them clinically indistinguishable in most cases. Internal monitoring is typically reserved for situations where the external tracing is difficult to obtain, such as with a very active baby or a mother with a higher body mass index.
For contractions, an internal pressure catheter can be placed inside the uterus to give true pressure readings in millimeters of mercury. The external belt can tell you when contractions are happening and how often, but it can’t accurately measure their strength.
Putting It All Together
When you look at a fetal monitor strip, work through a quick mental checklist. Start with the baseline heart rate on the top graph: is it between 110 and 160? Then look at the variability: does the line have that healthy zigzag? Check for accelerations, the reassuring upward spikes. Then look at the relationship between the top and bottom graphs: when contractions rise on the bottom tracing, what happens to the heart rate on top? If the heart rate dips, note the timing and shape of the dip to identify whether it’s early, late, or variable. Finally, check the contraction pattern on the bottom graph for frequency and regularity.
A reassuring strip shows a baseline of 110 to 160 bpm, moderate variability, the presence of accelerations, and no late or significant variable decelerations. The more of these features you see, the more confident the care team can be that the baby is tolerating labor well.