A fetal stress test is performed on pregnant women to measure the baby’s heart rate and movement. The test involves placing two belts on the woman's belly. One measures the fetal heart rate and the other measures contractions. Usually, this type of exam takes 20 to 30 minutes to perform and is given to women who are at least 28 weeks pregnant.
Doctors may administer a fetal stress test if the mother is concerned that the baby is not moving as frequently as usual or is not moving at all. A fetal stress test may also be performed if a pregnant woman is past her due date or if there is a problem with the placenta. If the mother-to-be is having a high-risk pregnancy, complications of any type can call for this exam.
Problems with the placenta or umbilical cord can often cause less oxygen to reach the baby. A fetal stress test can pick up on these problems. Placental and umbilical-cord issues that are detected on a fetal stress test can also be indicators of more serious fetal distress.
Doctors performing the test are looking for the baby’s heart rate to respond to movement. The heart rate of a healthy baby will increase during movement and will decrease at rest. If this is the case, the baby is getting the appropriate amount of oxygen. When oxygen levels are low, however, the baby will not respond appropriately to movement.
Women who are 28 weeks pregnant or more are candidates for fetal stress tests. Generally, doctors do not perform the test before then because the fetus is not sufficiently developed to respond to the exam. The fetal stress test is a noninvasive procedure that is free of risks or side effects to both the woman and the baby.
Most tests are performed in the doctor’s office. The nurse or doctor will hook up the fetal monitoring equipment to the woman’s belly and it will record the baby’s heart rate and movement. Some equipment may allow the pregnant woman to push a button when she feels the baby move. This helps doctors observe the relationship between the movement and the heart rate.
Sometimes, babies will not cooperate with the test. If the baby isn’t moving, the woman may be offered a drink with sugar or carbonation to wake up the baby. Creating a loud sound is another option used to perk up the baby.
Results of a fetal stress test are classified as reactive or nonreactive. Reactive means the blood flow and oxygen levels reaching the baby are in the correct range. A nonreactive outcome usually will result in additional testing to determine the reason for the lack of fetal movement. Possible reasons for a nonreactive result include poor oxygenation, sleep patterns, prescriptions taken by the pregnant woman, or nonprescription drugs.