What Are the Two Common Tests Used to Monitor Fetal Health?

As discussed in previous posts, various tests are available to monitor the health of a pregnancy and assess fetal well-being. These tests help screen for potential abnormalities and guide appropriate interventions. Some are routine screenings recommended for all pregnant individuals regardless of risk factors at specific milestones. These are recommended based on extensive research and public health guidelines derived from long-term studies across diverse populations. Other tests may be ordered based on individual risk factors or abnormal findings from initial studies.

In this post, we’ll explore two widely used screening tests—the Nonstress Test (NST) and the Biophysical Profile (BPP)—to provide a clearer understanding of their role in prenatal care. These tests become particularly common toward the end of pregnancy and play a key role in decisions about delivery methods.

Nonstress Test (NST)

The Nonstress Test, commonly abbreviated as NST, is a standard tool for monitoring fetal heart rate (FHR) and its response to stimuli, such as uterine contractions. During the test, probes are placed on the mother’s abdomen to measure FHR and track contractions. The procedure typically lasts at least 20-30 minutes but may be extended to ensure a thorough evaluation of any unusual readings. 

The NST provides key insights, including: 

• Baseline FHR: Normally ranges between 110 and 160 beats per minute. 
• FHR Variability: Fluctuations from the baseline, typically between 5 and 25 bpm. 
• Accelerations: Temporary increases in FHR, usually exceeding 15 bpm, often indicating fetal movement—a reassuring sign of a healthy baby.
• Decelerations: Temporary drops in FHR, which may vary in timing and significance.

The test also examines the relationship between accelerations or decelerations and uterine contractions.

Accelerations are commonly triggered by fetal movement, though contractions can also play a role. If accelerations are absent, healthcare providers may use techniques like fetal scalp stimulation or repositioning the mother to encourage a response. Persistent lack of acceleration despite these efforts could signal underlying issues requiring further investigation. 

Decelerations are classified into several types, each linked to different causes: 

• Early Decelerations: Occur in sync with contractions, almost mirroring them, and are typically benign, often due to head compression.
• Simple Variable Decelerations: Unrelated to contractions, usually caused by umbilical cord compression, and often resolve naturally.
• Complicated Variable Decelerations: Also unrelated to contractions but may indicate chemical changes in fetal blood, such as acidosis.
• Late Decelerations: Occur after contractions and may suggest uteroplacental insufficiency—a potentially serious condition.

While early or simple variable decelerations can be normal, other types, like late or complicated variable decelerations, may necessitate intervention to relieve fetal stress.

Biophysical Profile (BPP)

The Biophysical Profile, or BPP, is another essential tool for evaluating fetal well-being. It uses a scoring system out of 8 (or 10 if paired with an NST) and combines ultrasound observations with, optionally, NST results. The ultrasound assesses fetal movement and amniotic fluid index, providing a comprehensive picture of fetal health.

The BPP evaluates four key aspects, assigning a score of 0, 1, or 2 to each:

• Fetal Body Movement: General activity of the fetus.
• Fetal Limb Movement: Specific movements of arms or legs.
• Fetal Breathing: Rhythmic breathing motions.
• Amniotic Fluid Index (AFI): Measures the volume of amniotic fluid surrounding the fetus in different pockets.

A score of 2 indicates a normal result, 1 is suspicious, and 0 is abnormal. A total score of 8/8 (or 10/10 with NST) is reassuring, suggesting a very low risk of fetal distress or death within the next seven days. A score below 8/8 may prompt additional testing or interventions to safeguard the fetus and pregnancy.

Summary

In conclusion, the NST and BPP are vital components of routine prenatal care, particularly as pregnancy nears its end. The NST tracks fetal heart rate and uterine contractions, while the BPP uses ultrasound to assess fetal movements and amniotic fluid levels. Together, these tests guide critical decisions about delivery and the next steps in care.

It’s important to remember that your healthcare provider is the best resource for understanding the NST, BPP, and their results.

We’d love to hear about your experiences with these tests and how they influenced your delivery choices. You are welcome to share in the comments, on our social media pages, or via email!