On a fetal monitor, a contraction appears as a hill-shaped curve on the bottom half of the paper strip or screen. The line rises gradually from a flat baseline, peaks into a rounded summit, then slopes back down. Each contraction forms its own hill, and during active labor these hills appear at regular intervals, creating a repeating mountain-range pattern.
How the Monitor Strip Is Laid Out
A standard fetal monitor displays two separate graphs stacked on top of each other. The top graph tracks the baby’s heart rate in beats per minute, typically scaled in intervals of 10 bpm. The bottom graph tracks uterine activity, which is where you see contractions. Darker vertical lines on the strip mark one-minute intervals, with lighter lines every 10 seconds, so you can quickly gauge how long a contraction lasts and how far apart they are.
If you’re watching a bedside screen rather than a paper printout, you’ll see the same two tracings scrolling in real time. The contraction tracing sits along the bottom, and each time the uterus tightens, you’ll watch the line climb upward and then fall back to baseline.
What a Single Contraction Looks Like
A contraction starts when the line begins rising from its resting level. It climbs steadily to a peak, holds briefly, then descends back to where it started. The whole shape is roughly symmetrical, like a bell curve. During active labor, each contraction typically lasts about 60 to 90 seconds from start to finish, so on the strip you’d see the hill span roughly 6 to 9 of those 10-second grid lines.
Between contractions, the line settles back to a flat resting baseline. When measured with an internal pressure catheter, that resting level sits around 8 to 12 mmHg. You want to see the line return fully to this baseline between each hill. If it stays elevated and never quite flattens out, the uterus isn’t getting a full rest period between contractions.
Contraction Frequency and Spacing
To figure out how often contractions are coming, you measure from the beginning of one hill to the beginning of the next. For example, if a contraction starts at minute 2 and the next one starts at minute 5, the frequency is every 3 minutes. Nurses document this as a range (for instance, every 2 to 3 minutes) rather than using vague terms like “occasional.”
During active labor, you’ll typically see 3 to 5 contractions in a 10-minute window. More than 5 contractions in 10 minutes, averaged over a 30-minute period, is considered excessive. This pattern is called tachysystole, and it signals that the uterus is contracting too frequently for the baby to recover between squeezes. When staff spot this pattern, they’ll take steps to give the uterus more rest.
True Labor vs. Braxton Hicks on the Monitor
True labor contractions create hills that are evenly spaced and progressively get closer together. The peaks also tend to grow taller over time as contractions intensify. You’ll see a clear, predictable rhythm: hill, flat, hill, flat, with the gaps between hills slowly shrinking.
Braxton Hicks contractions look different. They appear as irregular bumps with no consistent spacing. One might show up, then nothing for 15 minutes, then two closer together, then another long gap. The peaks don’t follow a trend of getting taller or more frequent. If you were to walk around or drink water and the bumps disappeared from the strip, those were practice contractions, not the real thing.
Why the Peak Height Can Be Misleading
Most labor monitoring uses an external sensor called a tocodynamometer, a pressure-sensitive disc strapped to your belly with an elastic belt. This device detects that a contraction is happening and shows its timing, but the height of the hill on screen doesn’t reliably reflect how strong the contraction actually is. The reading depends heavily on how tightly the belt is secured, where the sensor sits relative to your uterus, and your body composition. Extra tissue between the sensor and the uterus can dampen the signal, making contractions look shorter on the monitor even when they’re quite strong.
This is why nurses often ask how the contraction feels to you, even though they can see it on the screen. They’ll also periodically press on your belly at the peak of a contraction to manually gauge its firmness. If accurate pressure measurements are needed, an internal pressure catheter can be placed after your water breaks. That device records actual pressure in mmHg and gives a true reading of contraction intensity.
What the Baby’s Heart Rate Shows During Contractions
While you’re watching the bottom tracing for contractions, the medical team pays close attention to how the top tracing (the baby’s heart rate) responds to each hill. The relationship between these two lines is one of the most important things on the entire strip.
A gentle dip in the baby’s heart rate that mirrors the contraction exactly, dropping at the start, hitting its lowest point right at the contraction’s peak, and recovering as the contraction ends, is called an early deceleration. These are common and considered harmless. They happen because the baby’s head gets briefly squeezed during the contraction.
A heart rate dip that starts late, reaching its lowest point after the contraction has already peaked and not recovering until well after the contraction ends, is a different story. These late decelerations suggest the placenta isn’t delivering enough oxygen during the squeeze. One or two may not be alarming, but a repeating pattern prompts the team to act quickly.
Sudden, sharp drops in heart rate that don’t follow a predictable pattern relative to contractions are called variable decelerations. These typically result from brief compression of the umbilical cord and are very common during labor. Occasional ones are usually fine, but deep or prolonged drops get immediate attention.
Reading the Numbers on the Screen
Most bedside monitors display a few key numbers alongside the scrolling tracings. You’ll typically see the baby’s heart rate updated in real time (a normal baseline falls between 110 and 160 bpm) and a number for uterine activity. With an external sensor, the uterine activity number is mostly useful for confirming that contractions are being detected. With an internal catheter, the number reflects actual pressure in mmHg, and contractions during active labor commonly peak between 40 and 80 mmHg above the resting baseline.
Some monitors also display contraction duration and frequency as calculated values. These update automatically, but your nurse will verify them by reading the strip directly, since the algorithms can occasionally miscount small fluctuations as contractions.