Non-stress Test

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  • Non-stress Test (NST)
    • evaluates four components of the fetal heart rate (FHR) tracing:
      • Baseline: Normally 110–160 beats/min.(MCQ)
      • Variability:
        • Beat-to-beat irregularity and waviness of the FHR.
        • Presence of variability reflects an intact and mature brain stem and heart. .(MCQ)
      • Periodic changes:
        • Early deceleration: .(MCQ)
          • Vagally mediated
          • caused by head compression usually at cervical dilation of 4–7 cm.
        • Variable deceleration .(MCQ)
          • caused by cord compression.
        • Late deceleration: .(MCQ)
          • Reflects hypoxemia.
      • Acceleration:
        • At least two accelerations of at least 15 beats/min above baseline for 15 sec in a 20-min period. .(MCQ)
        • Presence of accelerations = fetal well-being.
    • Reactive NST = two or more accelerations over 20 min.
      • Uterine contractions are also recorded to help interpret the NST.
      • Preterm fetuses are frequently nonreactive:
        • 24–28 weeks: Up to 50% nonreactive.
        • 28–32 weeks: 15% nonreactive.
        • An NST usually takes 20–40 min to complete
      • If the NST is nonreactive, the baby may be asleep
        • If this is suspected, ask the patient to eat or drinkto make the baby active if not reactive within 1–2 hours, then additional testing may need to be performed.
  • Contraction Stress Test (CST)
    • measures how the fetal heart rate (FHR) reacts to uterine contractions
    • The CST can be performed if the NST is nonreactive.
    • The FHR and the contractions are recorded simultaneously.
      • During a contraction, the blood flow to the placenta briefly 
      • A well-oxygenated fetus can compensate, and there are no decels in the FHR. .(MCQ)
      • If the fetus is already compromised with low levels of oxygen, the contraction may cause a late deceleration in FHR, which reflects hypoxemia in the fetus.
    • Patient is placed in lateral recumbent position and contractions are stimulated. .(MCQ)
      • Administration of oxytocin
      • Nipple stimulation (2 min self-stimulation through clothes every 5 min).
    • Adequate contractions: .(MCQ)
      • Occur three times in 10 min.
      • Lasting at least 40 sec.
    • Unsatisfactory: Fewer than three contractions in 10 min. .(MCQ)
    • Interpreted as the presence or absence of late decelerations: .(MCQ)
      • Negative: No late or significant variable decelerations.
      • Positive: Late decelerations following 50% or more of contractions.
      • Equivocal: Intermittent late decels or significant variable decelera-
      • tions.
    • Contraindications: .(MCQ)
      • Preterm labor patients at high risk of delivery.
      • Premature rupture of membranes (PROM).
      • History of extensive uterine surgery or previous cesarean section.
      • Known placenta previa
  • Biophysical Profile (BPP)
    • A biophysical profile (BPP) is the combination of the non-stress test and an ultrasound exam
    • It has total of five components: .(MCQ)
      • NST: Appropriate variation of fetal heart rate.
      • Breathing:
        • G>1 episode of rhythmic breathing movements of 30 sec or more within 30 min.
      • Movement:
        • G>3 discrete body or limb movements within 30 min.
      • Muscle tone:
        • G>1 episode of extension with return to flexion or opening/closing of a hand.
      • Determination of amniotic fluid volume:
        • Single vertical pocket of amniotic fluid measuring g>2 cm is considered adequate  or an amniotic fluid index g> 5 cm).
    • Scoring : .(MCQ)
      • Each of the category is given a score of 0 or 2 points:
      • 0: Abnormal, absent, or insufficient.
      • 2: Normal and present as previously defined.
      • Total possible score is 10 points.
      • Normal score: 8–10.
      • Equivocal: 6.
      • Abnormal: < 4.
      • In the presence of oligohydramnios (largest pocket of amniotic fluid <  2 cm), further investigation is required.
  • Doppler Velocimetry
    • Doppler sonography is a noninvasive technique used to assess fetal hemodynamic vascular resistance by imaging specific fetal vessels: .(MCQ)
      • Umbilical artery (UA) and umbilical vein.
      • Aorta.
      • Heart.
      • Middle cerebral artery (MCA).
    • Commonly measured flow indices are:
      • Peak systolic frequency shift (S).
      • Peak diastolic frequency shift (D).
      • Mean peak frequency shift over the cardiac cycle (A).
      • Systolic to diastolic ratio (S/D).
      • Resistance index (S-D/S).
      • Pulsatility index (S-D/A).
    • Flow velocity waveforms differ in normal-sized fetuses as compared to those suffering from growth restriction:
      • Fetuses with normal growth: .(MCQ)
        • High-velocity diastolic flow.
      • Fetuses with restricted growth: .(MCQ)
        • ivelocity diastolic flow,
        • hflow resistance (hS/D) in umbilical artery
        • iresistance (iS/D) in MCA.
      • Very severe intrauterine growth restriction.(MCQ)
        • Flow may be absent or even reversed.
    • Abnormal flow is usually the result of placental insufficiency and dysfunction, resulting in fetal hypoxia and acidosis.
    • This may induce the phenomenon of brain sparing: .(MCQ)
      • hS/D in umbilical artery (hresistance).
      • iS/D in MCA (iresistance).
  • Clinical Pearls
    • Most common cause of size not equal to date—incorrect gestational age. .(MCQ)
    • A reactive NST has two or more accelerations over 20 min = fetal well-being. .(MCQ)
    • When can a baby’s heartbeat be detected with Doppler?
    • 8–12 weeks of gestation Fetal heart starts beating at 22–24 days.(MCQ)
    • Modified BPP (mBPP) = NST + AFI.(MCQ)
    • Most common cause of Oligohydramnios = rupture of membranes.
    • “Brain sparing” may occur in hypoxic fetuses = increasedS/D in umbilical artery + decreasedS/D in middle cerebral artery. .(MCQ)


NonStress Test Made Simple
This video covers the basics of the NST (nonstress test)
Medical Video Lecture, OBGYN: NONSTRESS TEST (NST) Normal,Reactive & Non reactive
Prepare for USMLE,UK,CANADIAN,AUSTRALIAN, NURSING & OTHER MEDICAL BOARD examinations around the globe with us.Understand the basics, concepts and how to answer wisely and score 99 in each step. we are here to help you. what you are waiting for
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