Nonstress test

Description
The nonstress test uses ultrasound (sound waves) to measure changes in your baby's heartbeat when it moves within your uterus. Normally, the heart rate increases when the baby moves.

Purpose
The nonstress test provides information about your baby's well-being. For example, it's used to identify when your baby may lack sufficient oxygen or be stressed in other ways.

Indications
The nonstress test is done when certain conditions exist that may put your baby at risk. Beginning between the 32nd and 34th week of pregnancy, your doctor may recommend a nonstress test one or more times a week for any of the following conditions:
high blood pressure or preeclampsia (a serious condition that causes elevated blood pressure and protein in the urine)
diabetes, heart disease or kidney problems
too much or too little amniotic fluid (the fluid that surrounds and protects the fetus in the womb)
decreased fetal movement
baby who is smaller than anticipated for his or her age
pregnancy that has continued after the 40th week (post-term)
twin or higher multiple pregnancy
Depending on the severity of risk to your baby, the test may be recommended as early as the 26th week or pregnancy.


Patient preparation
Because a high blood sugar level may increase your baby's movement, you may be asked to eat an hour or two before the test.

Procedure
During the test, you'll lie down and an ultrasound transducer (an instrument that transmits sound waves) will be secured to your abdomen with an elastic strap. Once you're comfortable, the transducer will be attached to an external monitor. The sound waves sent by this instrument bounce off your baby to detect the heartbeat, which is then recorded by the monitor on a graph.
During the test, you may be asked to push a button whenever you feel movement. Your baby's movement may be spontaneous or stimulated by contractions or an external stimulus, such as a sound or rubbing your abdomen. At times, the baby's heart rate may speed up even though you have not felt a movement.

Depending on your baby's activity and the heart rate pattern, the test may take 20 to 40 minutes to complete. It may take longer if your doctor suspects that your baby is sleeping. It may be possible to awaken a sleeping baby by making a loud noise near the abdomen. Or, you may be asked to eat or drink something.

The desired outcome of a nonstress test is for your baby's heart rate to speed up for a brief time at least twice during a 20-minute period. This is known as a reactive nonstress test. Your doctor will end the test when sufficient increases in heart rate are detected.

The test is considered nonreactive when no increases in heart rate are detected or when the heart rate decreases. If the test is nonreactive, your doctor may recommend further testing, such as a contraction stress test (observing the pattern of your baby's heart rate during and after contractions).

When done before 28 weeks of gestation, up to 50 percent of women have nonreactive results due to immature fetal development rather than an actual problem. From 28 to 32 weeks of gestation, as many as 15 percent of nonreactive results may be related to immaturity. A nonreactive test can also be caused by certain maternal factors, such as central nervous system depression from low blood sugar or the use of sedatives, pain relievers or alcohol.


Postprocedure care
Discuss the test results with your doctor. Make sure you understand the test results and the amount of risk, if any, to the health of your baby. Your doctor may also have suggestions for follow-up care or delivery.

Benefits
The nonstress test is safe and noninvasive (nothing is introduced into your body). A reactive test can provide reassurance of a healthy baby at the time of the test. The findings may benefit prenatal care and delivery.

Risks
Rarely, a nonstress test may produce a false-normal result. An unpredictable complication that affects the health of your baby may develop at a later date. Nonreactive tests can't identify specific illnesses, which may cause anxiety for parents. In addition, up to 80 percent of nonreactive tests are eventually determined to be normal variants, which can also create unnecessary concern for parents.