When Is an NST Done in Pregnancy and Why?

An NST (nonstress test) is usually done during the third trimester when a healthcare provider wants to monitor a baby's well-being more closely. However, there is no fixed week when every pregnant woman needs an NST.

An NST may be recommended if there is reduced fetal movement, high blood pressure or preeclampsia, diabetes, concern about fetal growth, a high-risk pregnancy, or pregnancy continuing beyond the due date.

For some pregnancies that require ongoing fetal surveillance, monitoring may begin around 32–34 weeks. In other situations, it may be recommended earlier or later. The timing depends mainly on why monitoring is needed and how the pregnancy is progressing.

When Is an NST Done in Pregnancy?

An NST is generally performed during the third trimester when fetal surveillance is medically indicated.

There is no universal NST schedule. Your doctor considers your health, your baby's condition, pregnancy history, and the reason for monitoring before deciding when an NST is appropriate.

For some pregnancies requiring regular fetal surveillance, testing may begin around 32–34 weeks. If a specific concern develops earlier, monitoring may be recommended sooner. Similarly, testing may continue later in pregnancy when ongoing surveillance is needed.

So, rather than thinking of an NST as a test that automatically happens at a particular week, it is better to think of it as a monitoring tool used when your healthcare team needs additional information about your baby's well-being.

In short: An NST is usually done in the third trimester when there is a medical reason to monitor the baby more closely. The exact timing varies from one pregnancy to another.

If you want to understand the complete test, including how it is performed and what the results mean, see our guide to NST test in pregnancy.

Why Is an NST Recommended During Pregnancy?

An NST monitors your baby's heart rate and its response to movement during the monitoring period.

Your doctor may recommend one when there is a reason to check your baby's well-being more closely.

Reduced fetal movement

A noticeable change in your baby's usual movement pattern can be a reason for fetal monitoring. Learn more about reduced fetal movement and when it should be assessed.

An NST may help your healthcare provider assess your baby's heart rate during the monitoring period.

If your baby's movements are significantly reduced or different from usual, contact your maternity care provider promptly. Do not wait for a scheduled NST or your next appointment.

High blood pressure or preeclampsia

High blood pressure and preeclampsia can increase the risk of pregnancy complications.

Depending on the severity of the condition and other risk factors, your doctor may recommend additional fetal surveillance. An NST may be part of that monitoring plan.

The timing and frequency depend on your individual clinical situation.

Diabetes during pregnancy

Diabetes can increase the risk of certain pregnancy complications.

Depending on factors such as blood sugar control, treatment, gestational age, and other risk factors, your healthcare provider may recommend additional fetal surveillance.

An NST may be included as part of that monitoring.

Concerns about your baby's growth

If an ultrasound suggests that your baby may not be growing as expected, your doctor may recommend closer monitoring. This may involve assessment for fetal growth restriction alongside other fetal surveillance.

An NST can be used alongside ultrasound and other assessments to provide additional information about fetal well-being.

High-risk pregnancy

Some pregnancies require closer monitoring because of maternal health conditions, pregnancy complications, previous pregnancy history, or concerns involving the baby.

In these situations, an NST may be included in the overall fetal surveillance plan.

Being classified as high-risk does not automatically mean that you need an NST. Your healthcare provider decides based on the specific circumstances.

Pregnancy beyond the due date

If pregnancy continues beyond the expected due date, your healthcare provider may recommend additional fetal monitoring.

An NST may be combined with other assessments to evaluate your baby's well-being as pregnancy continues.

The exact monitoring plan depends on your pregnancy and your doctor's assessment.

Other maternal or fetal concerns

An NST may also be recommended when another maternal or fetal condition requires closer observation.

Your healthcare provider may consider your medical history, gestational age, ultrasound findings, fetal movement, and previous test results when deciding whether monitoring is appropriate.

How Does a Doctor Decide When to Start NST Monitoring?

Your doctor does not look at your pregnancy week alone.

They may consider:

• Your medical and pregnancy history

• Your baby's usual movement pattern

• Blood pressure and other maternal health conditions

• Ultrasound findings

• Your baby's growth

• Gestational age

• Previous monitoring results

• Other pregnancy-related risk factors

This is why two women at the same stage of pregnancy can have very different monitoring plans.

One may not need an NST, while another may need regular fetal surveillance.

The reason for monitoring is usually more important than reaching a particular week of pregnancy.

How Often Is an NST Done?

There is no standard NST schedule for every pregnancy.

Some women may need one NST because of a specific concern. Others may have regular monitoring when ongoing fetal surveillance is recommended.

Depending on the situation, your doctor may recommend testing once a week, twice a week, or at another interval.

The frequency may change based on:

• Why the NST was recommended

• Your pregnancy risk factors

• Your baby's condition

• Previous monitoring results

• Ultrasound findings

• How your pregnancy is progressing

If you have been asked to have regular NSTs, ask your healthcare provider how often you need monitoring and what they are looking for during each test.

Does Needing an NST Mean Something Is Wrong?

Not necessarily.

Being asked to have an NST does not automatically mean that there is a problem with your baby.

Your doctor may recommend one because your pregnancy has a risk factor or because they want additional information about your baby's well-being.

For example, monitoring may be recommended because of reduced fetal movement, a maternal health condition, concerns about fetal growth, or pregnancy continuing beyond the due date.

An NST is a way to check and monitor fetal well-being. It is not, by itself, proof that something is wrong.

Does an NST Mean I Will Need to Be Induced?

No. An NST does not automatically mean that you will need to be induced.

Your healthcare provider considers the NST findings alongside your symptoms, pregnancy history, gestational age, ultrasound findings, and other clinical information.

If the results raise a concern, your doctor may recommend additional monitoring or testing. In some situations, delivery may eventually be considered, but that decision is based on the overall clinical picture, not simply on having an NST.

When Should You Contact Your Doctor?

An NST is only one part of pregnancy monitoring. You should not wait for your next scheduled test if something concerning happens.

Contact your maternity care provider promptly if:

• Your baby's movements are noticeably reduced or different from usual

• You develop symptoms that concern you

• Your healthcare provider has given you specific instructions about when to seek care

In particular, a significant change in your baby's usual movements should be assessed promptly.

Do not use a home heartbeat monitor or another device as a substitute for medical assessment when you are concerned about reduced fetal movement.

Frequently Asked Questions

1. What week is an NST usually done?

An NST is generally performed during the third trimester when fetal surveillance is medically indicated. For some pregnancies requiring ongoing monitoring, it may begin around 32–34 weeks, but the timing can vary depending on the reason for testing.

2. Can a low-risk pregnancy need an NST?

A healthy, uncomplicated pregnancy does not automatically require an NST. However, your healthcare provider may recommend one if a concern develops or if additional fetal monitoring becomes appropriate.

3. How often might NST monitoring be repeated?

The frequency varies between pregnancies. Some women may need one test, while others may have regular monitoring. Your healthcare provider will determine the schedule based on why surveillance is needed and how the pregnancy is progressing.

4. What happens if an NST is nonreactive?

A nonreactive NST does not automatically mean there is a problem. Your healthcare provider may continue monitoring or recommend additional assessment based on the tracing, gestational age, and overall clinical situation.

For a detailed explanation, read NST Test Results: Reactive vs Non-Reactive Explained.

5. Is an NST the same as a CTG?

NST and CTG are related forms of fetal monitoring, but they are not always used interchangeably. An NST focuses on the baby's heart rate response during monitoring, while CTG generally records fetal heart rate together with uterine activity.

For a detailed comparison, read NST vs CTG.

Key Takeaway

An NST is usually done during the third trimester when your healthcare provider wants to monitor your baby's well-being more closely.

There is no single week when every pregnant woman needs an NST. For some pregnancies requiring ongoing fetal surveillance, monitoring may begin around 32–34 weeks, while other situations may require earlier or later testing.

An NST may be recommended because of reduced fetal movement, high blood pressure or preeclampsia, diabetes, concerns about fetal growth, a high-risk pregnancy, or pregnancy beyond the due date.

If your doctor recommends an NST, ask:

1. Why do I need this monitoring?

2. When should I have it?

3. Will I need repeat monitoring?

Understanding why monitoring has been recommended can help you feel more informed and prepared throughout your pregnancy.

Medical Review

Written by: Janitri Editorial Team
Medically reviewed by: Dr. Shreshtha Gupta, MBBS, MD/DNB – Obstetrics & Gynaecology
Last medically reviewed: August 2026