Overview
This lecture explains key diagnostic procedures in pregnancy: nonstress test (NST), biophysical profile (BPP), and contraction stress test (CST), including their methods, interpretation, and significance.
Nonstress Test (NST)
- An NST monitors fetal heart rate and uterine activity without stressing mother or baby.
- Two monitors are used: a tocometer (for contractions) and a fetal heart rate transducer (ultrasound or Doppler).
- Sometimes, the mother is given a button to mark fetal movements she feels.
- A "reactive" NST is desired: at least two increases (accelerations) in fetal heart rate of 15 bpm for 15 seconds within 20 minutes.
- "Non-reactive" NST means insufficient accelerations; further testing is needed.
- NST is performed for reasons such as decreased fetal movement, high-risk pregnancy, advanced maternal age, or post-dates.
Biophysical Profile (BPP)
- BPP combines NST and ultrasound to assess fetal well-being in five categories: NST result, fetal breathing, gross body movement, fetal tone, and amniotic fluid volume.
- Each category is scored 0 or 2, for a total of up to 10 points.
- A score of 8-10 is normal/reassuring; less than 8 indicates potential fetal hypoxia and may warrant delivery.
- Assesses: reactive NST, ≥1 breathing movement in 30 sec, ≥3 gross movements, ≥1 tone change, and ≥1 fluid pocket ≥2 cm.
Contraction Stress Test (CST)
- CST intentionally induces uterine contractions to assess fetal response (via nipple stimulation or oxytocin).
- Measures fetal heart rate during three contractions in 10 minutes.
- A "negative" CST (no late decelerations) is desired and reassuring.
- A "positive" CST (late decelerations in ≥50% of contractions) suggests placental insufficiency and is concerning.
- CST is less commonly performed due to risks and the availability of BPP.
Key Terms & Definitions
- Nonstress Test (NST) — Assessment of fetal heart rate in response to movement without stress to fetus/mother.
- Biophysical Profile (BPP) — Combination of NST and ultrasound scoring to evaluate fetal health.
- Contraction Stress Test (CST) — Test that evaluates fetal heart rate during induced contractions.
- Reactive NST — Fetal heart rate accelerates as expected; indicates good oxygenation.
- Non-reactive NST — Fetal heart rate doesn't sufficiently accelerate; may need further testing.
- Late deceleration — Slowing of fetal heart rate after contraction, may indicate low oxygen.
Action Items / Next Steps
- Review and memorize NST, BPP, and CST criteria and scoring.
- Study the definitions of key terms.
- Prepare for exam questions on indications and interpretation of NST, BPP, and CST results.