A nonstress test is used to evaluate a baby's health before birth. The goal of a nonstress test is to provide useful information about your baby's oxygen supply by checking his or her heart rate and how it responds to your baby's movement. The test might indicate the need for treatment or delivery to prevent fetal death.
Normally, a baby's heart beats faster when he or she is active later in pregnancy. However, conditions such as fetal hypoxia — when the baby doesn't get enough oxygen — can disrupt this pathway.
Your health care provider will decide whether a nonstress test is needed based on several factors. These include whether your baby could survive if delivered early, the severity of your condition and the risk of pregnancy loss.
Your health care provider might recommend a nonstress test if you have:
- A multiple pregnancy with complications
- An underlying medical condition, such as type 1 diabetes, high blood pressure, a blood disorder, lupus, thyroid disease, kidney disease or heart disease
- A pregnancy that has extended two weeks past your due date (postterm pregnancy)
- A history of pregnancy loss
- A baby who has decreased fetal movements or possible fetal growth problems
- Too much amniotic fluid (polyhydramnios) or low amniotic fluid (oligohydramnios)
- Rh (rhesus) sensitization — a potentially serious condition that can occur, typically during a second or subsequent pregnancy, when your blood group is Rh negative and your baby's blood group is Rh positive
- Worrisome results from other prenatal tests
Your health care provider might recommend having nonstress tests once or twice a week — and occasionally daily — depending on your and your baby's health. For example, you might need to have regular nonstress tests if your health care provider suspects that your baby is at risk of not getting enough oxygen. You might also need another nonstress test if you or your baby has any negative changes in health.