### Date : 2024-12-15 13:06 ### Topic : Non-stress test (NST) #OBGY ---- ### **Non-Stress Test (NST)** A **Non-Stress Test (NST)** is a simple and widely used **fetal monitoring** test to assess the well-being of a fetus, particularly in **high-risk pregnancies**. It is primarily used to monitor the **fetal heart rate** and determine how well the fetus is coping with the environment inside the womb, such as in conditions where there may be concern about **fetal growth** or **oxygenation**. ### **Purpose of the Non-Stress Test** The main goal of the **NST** is to evaluate how well the fetus is receiving oxygen and whether the **fetal heart rate** shows any signs of distress. It is called a **"non-stress"** test because it does not involve any **stress** on the fetus, such as through **contractions** or other stimuli. ### **Indications for NST** An NST is usually performed when there are concerns about **fetal health**, and it is often done in the following situations: 1. **Post-term pregnancies** (after 40 weeks of gestation). 2. **High-risk pregnancies** (e.g., maternal hypertension, diabetes, or preeclampsia). 3. **Decreased fetal movements** or suspected fetal distress. 4. **Multiple gestations** (twins, triplets, etc.). 5. **Fetal growth restriction (FGR)**. 6. **Complicated pregnancies** such as **placental insufficiency** or **maternal obesity**. 7. **Previous stillbirth** or other pregnancy complications in previous pregnancies. 8. **Oligohydramnios** (low amniotic fluid). ### **How the Non-Stress Test Works** The **NST** involves using a **fetal heart rate monitor** (also called a **doppler ultrasound** or **external fetal monitor**) to observe the fetus' heart rate pattern. 1. **Preparation**: - The mother is asked to lie down or sit comfortably. - Two external sensors are placed on the mother’s abdomen: - One sensor monitors the **fetal heart rate**. - The other sensor measures **uterine activity** (contractions) but is not always necessary for an NST. 2. **Monitoring**: - The fetal heart rate is continuously recorded over a period of **20-40 minutes** (sometimes longer, depending on the fetal activity). - The mother may be asked to press a button whenever she feels fetal movements, so these movements can be correlated with the fetal heart rate. 3. **Criteria for a "Reactive" NST**: - A **reactive NST** is considered **normal** and indicates that the fetus is likely to be well-oxygenated and not in distress. It is characterized by: - At least **2 accelerations** in the fetal heart rate of at least **15 beats per minute** (bpm) above the baseline. - These accelerations should last for **15 seconds or longer** within a **20-minute window**. 4. **Criteria for an "Non-Reactive" NST**: - A **non-reactive NST** occurs when the fetal heart rate does not show the required **accelerations** within the monitoring period (usually **20 minutes**). A non-reactive result does not necessarily indicate a problem but may require further testing or monitoring, such as: - **[[Biophysical profile (BPP)]]**. - **Contraction stress test (CST)**. - **Fetal movement counting**. - **Ultrasound** for further evaluation of fetal health. ### **Interpretation of NST Results** - **Reactive NST**: Indicates that the fetus is healthy and well-oxygenated. This result is typically reassuring and suggests that the fetus is not in distress. - **Non-Reactive NST**: Suggests that the fetal heart rate did not meet the criteria for normal accelerations. While this result is not definitive for fetal distress, it requires further investigation, which may include additional testing (e.g., **biophysical profile**, **ultrasound**, or **amniocentesis**). ### **Advantages of the Non-Stress Test** 1. **Non-invasive**: No harm is done to the fetus or the mother during the test. 2. **Simple and quick**: It can be performed relatively easily and provides real-time information on fetal well-being. 3. **Safe for the fetus**: There is no need for any invasive procedures or manipulation of the uterus. 4. **Widely available**: NST is a commonly performed test in labor and delivery units, clinics, and outpatient settings. ### **Limitations of the Non-Stress Test** 1. **False-positive results**: The test can sometimes show abnormal results even if the fetus is healthy. This can lead to unnecessary interventions or further testing. 2. **False-negative results**: It is possible for the NST to show normal results even when the fetus is in distress, especially if the baby is asleep during the test or is not moving much. 3. **Limited information**: NST focuses primarily on the **fetal heart rate** and **movement patterns**, but it does not provide comprehensive information about the overall condition of the fetus, such as the level of amniotic fluid or the placenta’s function. ### **Clinical Use of NST** NST is part of a broader approach to fetal monitoring. If the **NST** is **non-reactive**, additional tests such as **biophysical profiles (BPP)** or **amniocentesis** may be conducted to assess fetal well-being more comprehensively. An abnormal NST result does not necessarily mean that the fetus is in danger, but it usually prompts further investigation to ensure that any potential issues are detected early and managed appropriately. ### **Conclusion** The **Non-Stress Test (NST)** is an important screening tool used to monitor fetal health and detect potential distress, especially in high-risk pregnancies. It involves monitoring the fetal heart rate for signs of healthy accelerations in response to fetal movements. A **reactive NST** is reassuring, while a **non-reactive NST** warrants further investigation to ensure that the fetus is healthy. Although it is not definitive, the NST is a valuable tool in the **prenatal monitoring** of the fetus, helping guide clinical decisions in the management of pregnancies. ### Reference: - ### Connected Documents: -