How Do You Read Contraction Monitor? Expert Tips

Reading a contraction monitor means tracking two separate numbers at once: how strong each contraction gets, and how much time passes from the start of one contraction to the start of the next. The strength number is measured in millimeters of mercury (mmHg). The timing is measured in minutes and seconds. Those two pieces of information tell your care team whether labor is progressing and whether the baby is tolerating it.

Most people focus on the strength number because it looks impressive. The timing and the baby’s heart rate pattern usually matter more. Here is how to read the screen without panicking at every peak.

What Are the Two Lines on a Contraction Monitor?

A standard contraction monitor displays two tracings side by side on the same strip of paper or screen. The top line shows the baby’s heart rate. The bottom line shows uterine activity, which is the contraction pattern.

The top line is called the fetal heart rate tracing. A normal baseline for a baby in the womb is typically between 110 and 160 beats per minute. This line should wobble slightly rather than stay perfectly flat. That wobble is called variability, and it is a sign the baby’s nervous system is responding normally.

The bottom line is the tocodynamometer tracing, often shortened to “toco.” It measures the frequency and approximate duration of contractions. When you feel a contraction, this line rises into a curve and then falls back down. The peak of that curve is what people call the strength of the contraction.

One important detail: the toco measures changes in the shape of your abdomen, not the actual pressure inside the uterus. An internal monitor called an intrauterine pressure catheter (IUPC) measures true pressure in mmHg. External monitors give an estimate. That difference matters when comparing numbers.

How Do You Read Contraction Monitor Numbers for Strength?

On an external monitor, contraction strength is usually shown as a number on a scale, often 0 to 100. That number is not a direct pressure reading. It is a relative measure of how much the abdomen changes shape during a contraction.

On an internal monitor, strength is measured in mmHg. A common reference point is that contractions around 25 mmHg above the resting baseline are generally noticeable, and stronger contractions register higher. But there is no single number that defines “strong enough.”

What matters more than any single peak is the pattern. Are contractions getting closer together? Are they lasting longer? Is the resting tone between contractions returning to baseline, or staying elevated? A uterus that never fully relaxes between contractions is a pattern your care team watches closely.

How Do You Time Contractions on a Monitor?

Contraction timing is read from the start of one contraction to the start of the next. This is called the frequency. It is not the gap between the end of one and the start of the next, which is a common mistake.

Duration is how long a single contraction lasts from start to finish. A typical contraction during active labor lasts about 45 to 60 seconds, though this varies widely.

If you are timing at home without a monitor, you can do the same thing with a clock or a contraction timer app. Write down the start time of each contraction, how long it lasts, and how strong it felt on a scale you define for yourself. That log is often more useful to your provider than a single number.

Here is a simple way to track it:

• Note the exact time the contraction begins.
• Note the time it ends.
• Note the time the next one begins.
• Subtract the start times to get frequency.
• Subtract start from end to get duration.

What Does the Baby’s Heart Rate Line Tell You?

The fetal heart rate line is where clinicians spend most of their attention. Certain patterns are reassuring, and others prompt closer monitoring or intervention.

Reassuring patterns include a baseline between 110 and 160 beats per minute, moderate variability, and accelerations, which are brief increases in heart rate. Accelerations are generally a good sign.

Patterns that raise concern include a baseline that stays above 160 (tachycardia) or below 110 (bradycardia), reduced variability, and decelerations. Decelerations are drops in heart rate that can happen with contractions. Some types are common and generally not worrisome. Others, particularly those that persist after a contraction ends, need prompt evaluation.

This is the part of the monitor that requires clinical training to interpret. If you are watching the screen and see the baby’s heart rate drop, tell your nurse. Do not try to decide on your own whether it is a problem.

What Is a Normal Contraction Pattern in Labor?

There is no single normal pattern because labor varies from person to person. What clinicians look for is a progression.

Early labor contractions tend to be irregular, spaced further apart, and shorter. As labor advances, they typically become more regular, closer together, and longer. In active labor, a common pattern is contractions every 2 to 5 minutes, lasting about 45 to 60 seconds, though this is a general guide and not a rule.

During pushing, contractions may come even closer together. The monitor helps the team see whether the uterus is resting enough between contractions to keep blood flowing to the placenta.

What Do the Numbers Not Tell You?

A contraction monitor cannot measure pain. Two people can have identical tracings and very different experiences. Strength on the screen does not predict how much a contraction hurts.

It also cannot tell you whether labor is progressing in terms of cervical change. That requires a physical exam. A monitor shows the pattern of contractions, not how much the cervix has opened or effaced.

External monitors are also affected by movement, position, and body habitus. If you shift in bed or the belt loosens, the tracing can change even if nothing about your labor has. That is one reason nurses adjust the belts so often.

When Should You Call Your Provider About Contractions?

Call your provider if you are before 37 weeks and having regular contractions, because that could signal preterm labor. Call if your water breaks, if you have bleeding, or if you notice a change in your baby’s movement.

If you are at term and contractions are getting stronger, longer, and closer together, that is usually a sign to head in. Many providers use a general guide of contractions every 5 minutes for about an hour, but your specific instructions may differ. Follow what your provider told you.

If you are wearing a monitor at home for any reason and you see something that worries you, do not wait. Call. The monitor is a tool, not a substitute for clinical judgment.

How Do You Read a Contraction Monitor Without Overreacting?

Watch the pattern, not a single peak. One strong contraction on the screen is not a problem. A pattern of contractions that never lets the uterus rest is.

Ask your nurse to explain what they are seeing. Most are happy to walk you through it. Understanding the two lines can make the experience less frightening.

Remember that the monitor is one piece of information. Your provider is also watching you, your baby, and how labor is progressing. The numbers support that assessment. They do not replace it.