Results of a nonstress test are considered:
- Reactive. Before week 32 of pregnancy, results are considered normal (reactive) if your baby's heartbeat accelerates to a certain level above the baseline twice or more for at least 10 seconds each within a 20-minute window. At week 32 of pregnancy or later, if your baby's heartbeat accelerates to a certain level above the baseline twice or more for at least 15 seconds each within a 20-minute window, the results are considered reactive.
- Nonreactive. If your baby's heartbeat doesn't meet the criteria described above, the results are considered nonreactive. Nonreactive results might occur because your baby was inactive or asleep during the test.
If the test is extended to 40 minutes and your baby's nonstress test results are nonreactive and you are 39 weeks pregnant (full term), your health care provider might recommend delivery. If you are not full term, your health care provider will likely do another prenatal test to further check your baby's health. For example:
- Biophysical profile. A biophysical profile combines a nonstress test with a fetal ultrasound that evaluates your baby's breathing, body movements, muscle tone and amniotic fluid level.
- Contraction stress test. This test looks at how your baby's heart rate reacts when your uterus contracts. During a contraction stress test, if adequate uterine activity doesn't occur on its own you will be given intravenous oxytocin or be asked to rub your nipples to induce uterine activity.
Your health care provider might also ask you to have another nonstress test later in the day. Keep in mind that a reactive result is far more likely to be correct than is a nonreactive result. If you have a nonreactive nonstress test and a second nonstress test that's reactive, the results of the second test are considered reliable.
Other possible causes of a nonreactive nonstress test result, besides the fetus being inactive or asleep, include decreased oxygen (fetal hypoxia), maternal smoking, maternal use of medications, and fetal neurologic or cardiac anomalies.
Rarely, during a nonstress test, problems with a baby's heart rate are detected that require further monitoring or treatment.
Be sure to discuss the results of your nonstress test with your health care provider and what they might mean for you and your baby.