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Nonstress Tests During Pregnancy

As you near the end of your pregnancy, your provider will want to check baby's health. Dr. Therese Tran shares what to expect during your nonstress test, and why they are so important.

nonstress test

A nonstress test (NST) is a noninvasive test performed in the third trimester that evaluates how baby’s heart rate pattern responds to its own movements and contractions. NST’s are recommended for certain high risk maternal or fetal conditions that may affect baby’s wellbeing and may begin between 32-37 weeks occurring once or twice a week until delivery.

What Can I Expect During the NST?

Prior to the NST, ensure you have eaten and are well hydrated so baby will be awake and active. Empty your bladder before the test, as it can 20 to 40 minutes or longer.

During the test, you will recline in a chair while a fetal heart rate monitor and contraction monitor are placed externally on the abdomen. If baby seems sleepy, the nurse may give you a little buzz from an acoustic stimulator, which emits a small sound and vibration to wake up the sleepy baby.

After your procedure, your provider will review your results and discuss them with you. If you have any questions or concerns for your provider, they may be addressed at this time.

Sounds Easy, but What Do My Results Mean?

Reactive NST

A reactive NST is a test that shows at least two heart rate accelerations and an increase of 15 beats per minute above baseline for at least 15 seconds each. This indicates a healthy, happy, and well-oxygenated baby.

Nonreactive NST

A nonreactive NST occurs when baby’s heart rate stays near its baseline throughout the duration of the test — which is not always a negative thing. Babies will have nap times where they don’t sleep or move much for a few hours at various times during the day. Sometimes, this can occur during the NST.

Some medications that make us sleepy, can also make baby sleepy too. If baby appears sleepy, the nurse will encourage you to drink cold water, change positions, and use the fetal acoustic stimulator to try to wake baby up. If baby wakes up and starts moving, this is reassuring, and no additional testing is needed. If the test continues to be non-reactive after attempts to wake baby up, a biophysical profile would be performed.

A biophysical profile (BPP) is an advanced test for fetal well-being using ultrasound. It measures amniotic fluid levels, looks for fetal breathing and movement, and a tone over a 30-minute period — with two points given for each measure. A perfect score of 8/8 indicates a healthy baby, while a BPP score of <4 is suggestive of fetal compromise and adverse fetal outcome.

If your NST is nonreactive and BPP is equivocal or concerning, you may be directed to proceed to the hospital for prolonged monitoring, admission, or repeated testing. In rare cases, early delivery may be indicated.

When Is an NST Recommended?

There are other times when an NST would be recommended, including but not limited to the following:

  • Advanced maternal age (>37 years old at due date)
  • IVF pregnancy
  • Gestational, Type 1, or Type 2 diabetes
  • Maternal obesity with BMI >35
  • Chronic or gestational hypertension
  • Preeclampsia
  • Twin pregnancies
  • Fetal aneuploidy or anomalies
  • Previous stillborn pregnancy
  • Pregnancy at >41 weeks gestation
  • Decreased fetal movement
  • Abdominal trauma from falls and motor vehicle accidents
  • Maternal substance abuse

No matter what stage you are in your pregnancy, The Iowa Clinic OB/GYN providers are here for it all. Visit our website or call 515.875.9290 to learn more.

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