What is a Non-Stress Test (NST)?
A non-stress test or NST is the external monitoring of the baby's heart beat and uterine contraction. An NST is a painless way to check the baby's well being. A woman who has an NST will lie on a chair with two elastic belts wrapped around the middle of her belly. One belt records the baby's heartbeat, while the other records uterine contractions and the baby's movement.
Why are women referred for NSTs?
Women are referred for NSTs for a variety of reasons. Some of these may include:
- Pregnancy induced hypertension, PIH (high blood pressure)
- Diabetes (pregnancy induced/gestational or diabetes before pregnancy)
- Twin pregnancies
- Rh sensitization (which can happen if mother has RH negative blood & father is RH positive)
- Unexplained elevated maternal serum alpha-fetoprotein (MSAFP) level
- Previous stillbirth (death of baby before it is born)
- History of premature labor
- Postdates (more than 41 weeks along)
- Intra-uterine growth restriction, IUGR (the baby grows more slowly than expected)
- Decreased fetal movement (Baby is not as active or moving as often as expected)
- Too much or too little amniotic fluid (the fluid in which the baby is floating)
- In some cases, following an amniocentesis
How long will an NST take, and when are they usually done?
Generally, an NST will last for 15 to 45 minutes. However, some tests may take longer. Non-stress tests may be done twice a week, after the 28th week of pregnancy.
What are we looking for in an NST?
A baby's heart rate generally increases when it moves. When this happens two or more times in a ten-minute interval, the test is considered "reactive". This reactivity lets us know the baby is receiving adequate oxygen at the time of the test. If the NST is "non-reactive," the physician may suggest additional tests, such as ultrasound or Biophysical Profile.
What if the baby is sleeping during the test?
If the baby is sleeping, the nurse may try to wake the baby by placing her hands on your belly, making a loud noise, or placing a vibrating device on the belly. None of these steps will hurt you or your baby.