Nonstress Test (NST)

The Nonstress test (NST) is a prenatal test used to check on the well-being of a baby, particularly in the third trimester of pregnancy. It measures the fetal heart rate in response to the baby's movements.

Purpose

The purpose of the NST is to:

• Assess fetal well-being and detect any potential problems
• Monitor the fetal heart rate and its response to movement
• Identify babies who may be at risk for complications, such as growth restriction or placental insufficiency

Procedure

The NST procedure typically involves:

• A pregnant woman lying on her back or side with a fetal monitor strapped to her abdomen
• A sensor that detects the fetal heart rate and movement
• A printout of the fetal heart rate tracing, which is analyzed for accelerations (increases in heart rate) and decelerations (decreases in heart rate)
• The test usually lasts between 20-40 minutes, although it may take longer if the baby is not active

Interpretation of Results

The results of the NST are interpreted as follows:

• Reactive: The test is considered reactive if there are two or more accelerations of at least 15 beats per minute (bpm) within a 20-minute period. This suggests that the baby is healthy and active.
• Nonreactive: If there are fewer than two accelerations, the test is considered nonreactive. This may indicate that the baby is sleeping or under stress, but it can also be a sign of potential problems.

Risks and Limitations

The NST is a non-invasive and safe procedure, but it has some limitations:

• False reassurance: A reactive test does not guarantee that the baby is healthy or that there are no underlying problems.
• False alarms: A nonreactive test may lead to further testing or interventions that may not be necessary.

Follow-up Testing

If the NST is nonreactive, follow-up testing may include:

• Biophysical profile (BPP): An ultrasound test that evaluates fetal movement, tone, breathing, and other parameters.
• Contraction stress test (CST): A test that measures the fetal heart rate in response to uterine contractions.

Frequently Asked Questions (FAQs)

What is a Nonstress test?
A prenatal test that measures fetal heart rate in response to movement.

Why is a Nonstress test performed?
To assess fetal well-being and detect potential distress or complications.

How long does a Nonstress test take?
Typically 20-40 minutes, but can vary depending on fetal movement.

Is a Nonstress test painful?
Generally no, it is a non-invasive and painless procedure.

What equipment is used for a Nonstress test?
A fetal monitor or cardiotocograph to track fetal heart rate.

Can a Nonstress test detect all fetal problems?
No, it has limitations and may not detect all potential issues.

How often are Nonstress tests performed during pregnancy?
Usually weekly or biweekly after 28 weeks of gestation, but frequency varies.

Are there any risks associated with a Nonstress test?
Generally no significant risks, but false reassurance or unnecessary interventions possible.

Can a Nonstress test be performed at home?
No, typically requires medical supervision and equipment in a clinical setting.

What is the significance of a reactive Nonstress test result?
Indicates normal fetal heart rate patterns, suggesting good fetal health, but not definitive.