Nonstress test

Nonstress Test

A nonstress test (NST) is a common prenatal test used to check on a baby's health. During a nonstress test, the baby's heart rate is monitored to see how it responds to the baby's movements. The term "nonstress" refers to the fact that nothing is done to place stress on the fetus during the test.

Purpose

The primary purpose of a nonstress test is to provide useful information about the baby's oxygen supply by checking the baby's heart rate and how it responds to movement. The test is typically performed in the third trimester of pregnancy, often after 28 weeks of gestation.

Indications

A nonstress test may be recommended for various reasons, including:

• High-risk pregnancy
• Gestational diabetes
• Hypertension or preeclampsia
• Decreased fetal movements
• Post-term pregnancy (beyond 40 weeks)
• Multiple gestation (twins or more)

Procedure

The nonstress test is a simple, non-invasive procedure. It involves the following steps:

1. The pregnant individual is asked to lie down or sit in a comfortable position. 2. Two belts with sensors are placed around the abdomen. One sensor measures the fetal heart rate, and the other measures uterine contractions. 3. The test usually lasts about 20 to 30 minutes, but it can take longer if the baby is not very active or asleep. 4. The heart rate is monitored to see if it increases with fetal movements, which is a sign of good health.

Interpretation

The results of a nonstress test can be classified as "reactive" or "nonreactive":

• Reactive (normal): The baby's heart rate increases by at least 15 beats per minute for at least 15 seconds, at least twice during a 20-minute period.
• Nonreactive: The baby's heart rate does not meet the criteria for a reactive result. This may require further testing, such as a biophysical profile or a contraction stress test.

Risks

The nonstress test is a safe procedure with no known risks to the mother or baby. It is a non-invasive test and does not involve any medications or procedures that could harm the fetus.

Limitations

While a nonstress test can provide valuable information about the baby's health, it is not definitive. A nonreactive result does not necessarily mean there is a problem, but it may indicate the need for further testing.

Also see

• Biophysical profile
• Contraction stress test
• Fetal monitoring
• Prenatal care