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Contraction Stress Test

A contraction stress test checks to see if your baby will stay healthy during contractions when you are in labor. This test includes external electronic fetal monitoring. The test is done when you are 32 or more weeks pregnant.

During a contraction, the blood and oxygen supply to your baby drops for a short time. This is not a problem for most babies. But the heart rate of some babies gets slower. This change in heart rate can be seen on the external fetal monitor.

For this test, you may be given the hormone oxytocin. This hormone causes uterine contractions. Or you may be asked to massage your nipples. This tells your body to release oxytocin. During this test, your baby's heart rate may slow down (decelerate) in a certain pattern after a contraction instead of speeding up (accelerating). This means your baby may have problems with the stress of normal labor.

A contraction stress test is usually done if you have an abnormal nonstress test or biophysical profile. A biophysical profile uses ultrasound during a nonstress test to measure a series of physical traits of your baby. You may have more than one contraction stress test while you are pregnant.

Some doctors may do a biophysical profile or a Doppler ultrasound test instead of a contraction stress test.

Why It Is Done

A contraction stress test is done to:

Find out if your baby will stay healthy during labor, when contractions reduce the oxygen levels.
Check to see if the placenta is healthy and can support your baby.

This test may be done when results from a nonstress test or a biophysical profile are not normal.

How To Prepare

Empty your bladder before the test.

If you smoke, stop for 2 hours before the test. Smoking can lower your baby's activity and heart rate.

You may be asked to sign a consent form that says you understand the risks of the test and agree to have it done.

How It Is Done

A contraction stress test may be done in your doctor's office or a hospital. It is done by a family medicine doctor or an obstetrician and a trained lab technician or nurse. You probably won't need to stay overnight.

During the test, you will lie on a bed with your back raised. You will be tilted a little to your left side. This is so you will not put pressure on the blood vessels in your belly. Two belts with sensors will be placed around your belly. One belt holds the sensor that records your baby's heart rate. The other sensor measures your contractions. Gel may be used on your skin with the heart rate sensors. The sensors are hooked to a recording unit. The heart rate monitor may be moved if your baby changes position.

Your baby's heart rate and your contractions are recorded. Your blood pressure and other vital signs are also recorded.

You may be given the hormone oxytocin in a vein (intravenously, or I.V.). It is started at a low dose. The dose is increased until you have three contractions within 10 minutes that each last longer than 45 seconds. Or you may be asked to massage one of your nipples by hand to start contractions. If you don't have a second contraction within 2 minutes of the first, you will rub your nipple again. If contractions do not occur within 15 minutes, you will massage both nipples.

After the test, you will be watched until your contractions stop or slow down to what they were before the test.

How long the test takes

A contraction stress test may take 2 hours.

How It Feels

You may have some discomfort during the contractions. And the belts that hold the sensors in place may feel tight on your belly. Most people say this test is uncomfortable but not painful.

Risks

Electronic fetal monitoring may show that your baby is having problems when your baby is healthy. It can't find every type of problem, such as a birth defect.

Using oxytocin also has risks.

It may cause labor to start sooner than your expected delivery date.
It may cause contractions that go on for a long time. This may cause problems with your baby. The contractions usually stop when the oxytocin is stopped. You may get a medicine to stop the contractions. In very rare cases, the contractions don't stop. If that happens, your doctor may suggest delivery.

Results

Results of the test help predict if your baby will stay healthy during labor for the upcoming week. The test may need to be done more than once during your pregnancy.

Normal. Normal test results are called negative. Your baby's heart rate does not get slower (decelerate) and stay slow after the contraction (late decelerations).Your baby is expected to be able to handle the stress of labor if there are no late decelerations in your baby's heart rate during three contractions in a 10-minute period.
Abnormal. Abnormal test results are called positive. Your baby's heart rate gets slower (decelerates) and stays slow after the contraction (late decelerations). This happens on more than half of the contractions.Late decelerations mean that your baby might have problems during normal labor.

A contraction stress test may show that your baby's heart rate slows down (decelerates) when your baby is not actually having problems. This is called a false-positive result.

Glossary

A biophysical profile (BPP) test measures the health of your baby (fetus) during pregnancy.

A BPP test includes a fetal ultrasound and usually includes a nonstress test. The BPP measures your baby's heart rate, muscle tone, movement, breathing, and the amount of amniotic fluid around your baby. Some BPPs do not include all the measurements.

A biophysical profile may be recommended if the results of a nonstress test are nonreactive. A nonreactive nonstress test means that the baby's heart rate did not change as expected when the baby moved. A biophysical profile may also be recommended for high-risk pregnancies. The tests allow the doctor to find any possible problems as early as possible.

The results of the biophysical profile can help the doctor know if the baby is healthy. The doctor may use the results of the BPP test to help decide when to deliver the baby or if a cesarean section is a safer way to deliver.

A Doppler ultrasound (or duplex scanning) is a medical test that uses reflected sound waves to estimate the speed and direction of blood as it flows through a blood vessel. It helps doctors evaluate blood flow through arteries and veins.

Doppler ultrasound can be used to evaluate the vessels in several areas of the body. For example, a Doppler ultrasound test of the blood vessels in the neck (carotid ultrasound) can be done to estimate a person's risk of a stroke from blockage in those arteries. Renal ultrasound can help detect kidney problems. Lower extremity ultrasound can be used to detect a blood clot in the deep veins of the legs. A Doppler ultrasound also may be used to evaluate problems with the blood flow to the placenta and umbilical cord during pregnancy. Problems with this blood flow may point to fetal distress.

Electronic fetal monitoring measures a baby's (fetus's) heart rate during pregnancy or labor and delivery. It also shows how long and how strong your contractions are. These measurements can help a doctor or midwife check if a fetus is healthy or having any problems.

During labor and delivery, the fetal heart rate is closely watched along with uterine contractions. This helps the doctor or nurse see how the baby is responding and whether any treatments are needed.

Two types of monitoring—external or internal—can be done.

For external monitoring, instruments that detect fetal heartbeats and your contractions are placed around your abdomen.
For internal monitoring, a thin wire (electrode) is put through your cervix and attached to your baby's scalp. A small tube may also be guided through your cervix and into your uterus to measure contractions. Internal monitoring is not done if there is placenta previa, a condition where the placenta is low and just above the cervix, because of the risk of bleeding.

External electronic fetal monitoring is done during pregnancy, labor, and delivery. It is done to keep track of the heart rate of your baby (fetus) and the duration of the contractions of your uterus.

A false-positive test result is one that appears to detect a disease or condition when in fact it is not present. A false-positive test result may thus suggest that a person has the disease or condition when they do not.

For example, a false-positive pregnancy test result would be one that appears to detect the substance (human chorionic gonadotropin) that would confirm pregnancy, when in reality the person is not pregnant.

Family medicine physicians, also called family practice physicians, are medical doctors who specialize in the total health care of the individual and the family. After four years of medical school, they complete an additional three-year residency program.

Family medicine physicians can diagnose and treat a variety of health conditions and diseases for all ages. They may further specialize in another area of medicine, such as the care of older adults (geriatric medicine) or people who have sports injuries (sports medicine).

Family medicine physicians can be board-certified by the Board of Family Medicine, which is recognized by the American Board of Medical Specialties.

Intravenous means occurring within or by way of a vein. Medicines or fluids may be given by inserting an intravenous (I.V.) needle into a vein, usually in the back of the hand or on the forearm.

When the I.V. needle is in place, medicines or fluids can go quickly into the bloodstream and into the rest of the body.

Obstetricians (also called OBs) are medical doctors who specialize in providing pregnancy care from the time of conception through delivery and the period following delivery (postpartum). Most obstetricians are also gynecologists who diagnose and treat diseases of the female reproductive system and provide care for those who are not pregnant.

An obstetrician can further specialize in perinatology (maternal-fetal medicine), which focuses on high-risk pregnancies, testing, and fetal development. Or an obstetrician may specialize in reproductive endocrinology and infertility (care of those who have hormonal or fertility problems).

Obstetricians can be board-certified through the Board of Obstetrics and Gynecology, which is recognized by the American Board of Medical Specialties.

The placenta is a large organ that develops in the uterus during pregnancy and is connected to the fetus by the umbilical cord. Through the blood vessels in the umbilical cord and placenta, the fetus receives oxygen and nutrients from the mother and gets rid of wastes.

The placenta is delivered soon after the baby is born. (This is sometimes called the afterbirth.)

Ultrasound is a test that uses reflected sound waves to produce an image of organs and other structures in the body. It does not use X-rays or other types of possibly harmful radiation.

For ultrasound testing, gel or oil is applied to the skin to help transmit the sound waves. A small, handheld instrument called a transducer is passed back and forth over the area of the body that is being examined. The transducer sends out high-pitched sound waves (above the range of human hearing) that are reflected back to the transducer. A computer analyzes the reflected sound waves and converts them into a picture that is displayed on a TV screen. The picture produced by ultrasound is called a sonogram, echogram, or ultrasound scan. Pictures or videos of the ultrasound images may be made for a permanent record.

Ultrasound is most useful for looking at organs and structures that are either uniform and solid (such as the liver) or fluid-filled (such as the gallbladder). Mineralized structures (such as bones) or air-filled organs (such as the lungs) do not show up well on a sonogram.

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