What does a reactive non-stress test (NST) indicate?
Fetal distress
Fetal well-being
Uteroplacental insufficiency
Cord compression
The Correct Answer is B
Non-stress test interpretation evaluates fetal heart rate patterns in response to movement, primarily assessing oxygenation, autonomic integrity, placental function, and neurologic status. In term fetuses, normal baseline fetal heart rate ranges from 110–160 bpm with variability of 6–25 bpm. A reactive NST shows accelerations of ≥15 bpm lasting ≥15 seconds, suggesting intact sympathetic and parasympathetic regulation and adequate fetal oxygenation.
Rationale for correct answers
B. A reactive non-stress test reflects fetal well-being. It indicates sufficient oxygen delivery via the placenta and intact autonomic response. The presence of at least 2 accelerations within a 20-minute window in term fetuses confirms reactivity and a reassuring status.
Rationale for incorrect answers
A. Fetal distress is typically associated with absent accelerations, decreased variability, or late decelerations. A reactive NST, by definition, rules out distress at the time of testing and suggests normal fetal acid–base balance.
C. Uteroplacental insufficiency manifests as absent accelerations, decreased variability, or late decelerations. These would lead to a non-reactive NST, not a reactive one, which implies that placental perfusion is adequate.
D. Cord compression leads to variable decelerations, not accelerations. If present, these would be noted during monitoring and may signal concern depending on frequency and severity. A reactive NST lacks these deceleration patterns.
Take home points
- Reactive NST suggests adequate fetal oxygenation and neurologic status.
- Requires 2 accelerations of ≥15 bpm lasting ≥15 seconds in 20 minutes.
- Non-reactive NST may signal placental or umbilical pathology.
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Related Questions
Correct Answer is B
Explanation
Fetal circulatory architecture establishes a placental-dependent system where oxygen delivery, waste removal, pressure gradients, and vascular routing are coordinated through specialized shunts. The umbilical arteries originate from the internal iliac arteries and carry blood with oxygen saturation approximately 50–60%. Fetal arterial PaO₂ is around 20–25 mmHg, significantly lower than postnatal arterial values of 80–100 mmHg. Low oxygen content is tolerated due to high fetal hemoglobin concentration.
Rationale for correct answers
B. The umbilical arteries are responsible for transporting deoxygenated, waste-laden blood from the fetus to the placenta. Their origin from the internal iliac arteries and their direct routing to the placenta supports excretory and respiratory exchange with maternal circulation.
Rationale for incorrect answers
A. The umbilical arteries do not deliver oxygenated blood. Instead, oxygenated blood is supplied to the fetus by the umbilical vein, which carries blood from the placenta with saturation levels around 70–80%. This blood bypasses hepatic circulation via the ductus venosus en route to systemic circulation.
C. The fetal lungs are bypassed by other shunting mechanisms—not the umbilical arteries. Structures like the foramen ovale and ductus arteriosus direct blood away from nonfunctional fetal lungs. The umbilical arteries are peripheral and not directly involved in this bypass system.
D. Nutrient absorption occurs via the placenta and maternal supply, not through the umbilical arteries. These arteries merely transport deoxygenated blood to the placenta, where nutrient and gas exchange occurs. They have no absorptive role.
Take home points
- Umbilical arteries carry deoxygenated blood from fetus to placenta.
- Oxygenated blood is supplied via the umbilical vein, not arteries.
- Fetal lungs are bypassed by cardiac shunts, not vascular exits.
- Nutrient absorption is a placental function, not arterial.
Correct Answer is ["A","B","D"]
Explanation
Biophysical profile (BPP) is a prenatal test used to assess fetal well-being by evaluating fetal heart rate, breathing movements, tone, and amniotic fluid volume. It combines ultrasound and non-stress test findings. Normal BPP scores range from 8–10, indicating low risk of fetal compromise, while scores below 6 suggest potential hypoxia or acidosis.
Rationale for correct answers
A. Fetal heart rate accelerations are assessed using a non-stress test, which evaluates the fetal response to movement. Two or more accelerations of at least 15 beats per minute lasting 15 seconds within 20 minutes are considered normal.
B. Fetal breathing movements are observed via ultrasound. Normal breathing movements include rhythmic diaphragmatic contractions lasting at least 30 seconds within a 30-minute observation period.
D. Fetal tone is assessed by observing movements such as limb flexion and extension. Normal tone includes at least one episode of active extension with return to flexion within 30 minutes.
Rationale for incorrect answers
C. Maternal blood pressure is not a component of the biophysical profile. While maternal health is critical for fetal well-being, blood pressure is assessed separately and does not directly contribute to the BPP score.
E. Cervical length is not evaluated in a biophysical profile. It is assessed during pregnancy to predict preterm labor risk but is unrelated to fetal well-being parameters measured in the BPP.
Take home points
- Biophysical profile evaluates fetal heart rate, breathing movements, tone, and amniotic fluid volume.
- Normal BPP scores range from 8–10; scores below 6 indicate potential fetal compromise.
- Maternal blood pressure and cervical length are not components of the BPP.
- BPP combines ultrasound findings with non-stress test results.
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