Preterm birth, or a birth that happens before 37 weeks of pregnancy, is the leading cause of infant death and health problems. True labor contractions are one of the symptoms of early labor, which can lead to preterm birth. If you are at high risk of preterm birth, your doctor may ask you to pay very close attention to persistent uterine tightenings or cramping that may signal premature contractions. Information about your contractions can help your doctor decide if you need to make changes to your pregnancy care plans.
This article explains what contractions are, how they are measured, and how paying attention to contractions can help prevent preterm birth.
To learn more about why preterm birth is an important issue in pregnancy, read Premature Birth 101.
How Are Contractions Measured?
Contractions are the tightening of the muscles of your uterus. They don’t feel the same to everyone, and different types are stronger than others. During labor, contractions help the baby move through the birth canal.
- Braxton Hicks contractions are mild contractions that are also called practice contractions or false contractions. These types of contractions usually do not result in cervical dilation. In patients at higher risk for premature birth, however, it is advisable to seek consultation with your care provider to be cautious.
- Active labor contractions are stronger contractions that make changes to your cervix and uterus to help your body get ready for delivery.
- Contractions during the second phase of labor are more intense. They help you deliver your baby (learn more about the stages of labor in this article from the National Institute of Health).
Doctors measure contractions by using a tocodynamometer—called a toco for short—a sensor that measures pressure. The toco sends a signal to a monitor, which measures contractions in units called mmHg, or millimeters of mercury. These are the common ranges of toco numbers for the three types of contractions:
- Braxton Hicks: 5-25 mmHg
- Active labor contractions: 40-60 mmHg
- Second phase contractions: 50-80mmHg
If you are having contractions and you can’t tell if they are Braxton Hicks or true labor contractions, you should call your doctor right away. They may recommend contraction monitoring at the office or hospital.
Measuring Contractions at the Office
Usually, your doctor will measure your contractions in their office or at the clinic or hospital. The doctor or nurse will place a toco on your belly, attached with a strap. The machine will send the data to a monitor that records your contractions.
How Is My Baby’s Heartbeat Monitored?
As your pregnancy moves forward, your doctor may want to learn how your baby is handling contractions. A normal heartbeat means that baby is doing fine, while an abnormal heartbeat could be a sign that they need to take other actions. This may include more tests, a change in your position, or an early delivery.
How Are Contractions Monitored in a High Risk Pregnancy?
In most pregnancies, there is no need for constant contraction monitoring. If you are at high risk of having a preterm delivery, your doctor may recommend more frequent contraction monitoring in the office or at the hospital.
Learn more about the PreTRM Test and how it helps doctors understand which pregnancies are at high risk of preterm delivery.
Types of Fetal Monitors
There are two main types of fetal monitors: external and internal monitors
External Heart Rate Monitoring
External fetal heart rate monitoring is the most common tool used for monitoring fetal heart rate and your contractions. It has two straps that are placed on the belly to measure uterine activity: one has a sensor to read the baby’s heartbeat, and the other measures how strong and frequent your contractions are. The monitor reads both sets of data to give doctors information about how well your baby is handling labor.
Internal Heart Rate Monitoring
Internal fetal heart rate monitoring is not used as often as external monitoring. Doctors use it when they need a more detailed information than they can get with external monitoring. Internal heart rate monitoring can only be done when your water has broken.
With internal monitoring, your doctor will place a thin wire through your vagina. It has a sensor on the end, which is placed on the baby’s scalp. This fetal heart monitoring sensor sends a detailed record of the baby’s heartbeat to the monitor. To measure your uterine contractions, the doctor will place a second tube in the uterus or attach a toco to your belly with an external strap.
Intermittent auscultation is when a doctor or nurse places a special stethoscope against your belly. This will let them check the baby’s heart rate from time to time during labor, to make sure the baby is not getting stressed out by contractions.
Electronic Fetal Monitoring
With electronic fetal monitoring, your healthcare provider will monitor your baby’s heartbeat during labor and delivery. They will place a sensor on your belly that sends a signal to a computer monitor.
There are a few possible reasons your doctor will start electronic fetal monitoring:
- If your doctor induces labor during pregnancy week 39 or 40. Sometimes your doctor will start your labor medically, for your health or the safety of your baby. Read more about labor induction in this article from the NIH.
- If you choose to get an epidural. Epidural medicine is a form of anesthesia used during delivery. Because it blocks the feeling of pain, your doctor may want electronic fetal monitoring to help them know when contractions are happening and to monitor heart rate activity.
- If you have other risk factors for preterm birth or other health problems.
Can Monitoring Contractions Reduce the Risk of Early Labor and Preterm Birth?
If you are at high risk of preterm birth, it is very important that you be extra vigilant for the signs of preterm birth. Your physician may want you to keep track of your contractions in addition to overall health indicators. This will help you work with your healthcare team to know which contractions are the mild “practice” contractions known as Braxton Hicks, and which may be having an effect on your cervix, possibly leading to an early delivery.
If your doctor thinks that your contractions may be changing your cervix to get it ready for delivery, they may give you an ultrasound. Learn more about ultrasound and other common pregnancy tests here.
Contraction Monitor FAQs
What is a contraction on the monitor?
On a monitor, the fetal heart rate is usually at the top left of the screen, and the contractions are on the right. When the monitor prints out the information on paper, each contraction looks like a bell-shaped curve.
What number should contractions be at on monitor?
During true labor, the toco numbers range from 40-60 mmHg at the beginning of the active phase of labor, and 50-80 mmHg during the second phase of labor, when your cervix is fully open. This may somewhat very, person to person based on body habitus and whether the monitors are placed external or internally.
Do Braxton Hicks show up on monitor?
Braxton Hicks contractions, or false contractions, have lower toco readings than true labor contractions. They are usually in the range of 5-25 mmHg.
Can you walk around with fetal monitoring?
When you have continuous external fetal monitoring, you may be allowed to walk around during labor. If the sensors are attached to the monitor with wires, that may limit your movement. There are wireless devices at some birthing centers, which give more freedom of movement during labor.
How can I monitor my contractions at home?
It is important to pay attention to the timing of your contractions. You should talk to your doctor if you can’t tell whether your contractions are Braxton Hicks “practice” contractions, or true labor contractions. It can be helpful to write down the time that each contraction starts and stops.
Talk to your doctor today about the PreTRM Test for your individual risk assessment.