EFM - Electronic Fetal Monitoring Maternal-Fetal Physiology Questions and Answers — Questions and Answers
Question 1: A laboring patient who received an epidural anesthetic rapidly develops hypotension. Which of the following fetal heart rate patterns is most likely to be observed as a direct result of this maternal change?
- Early decelerations
- Late decelerations (Correct answer)
- Variable decelerations
- Marked variability
Correct answer: Late decelerations
Maternal hypotension reduces blood flow to the uterus and placenta, a condition known as uteroplacental insufficiency. This decrease in perfusion leads to fetal hypoxia, which stimulates fetal chemoreceptors and results in a reflex slowing of the heart rate. Because this response is tied to the period of decreased oxygen delivery during a contraction, the deceleration's onset is delayed relative to the contraction's peak, which is characteristic of a late deceleration.
Question 2: Which physiological mechanism is primarily responsible for the presence of moderate variability in the fetal heart rate?
- The interplay between the sympathetic and parasympathetic nervous systems (Correct answer)
- Stimulation of fetal baroreceptors due to blood pressure changes
- The release of catecholamines from the adrenal medulla
- Fetal movement and behavioral state changes
Correct answer: The interplay between the sympathetic and parasympathetic nervous systems
Moderate variability, the fluctuations in the fetal heart rate baseline, is a direct reflection of a healthy, intact, and well-oxygenated fetal central nervous system. It is produced by the continuous and balanced push-and-pull interaction between the sympathetic (acceleratory) and parasympathetic (deceleratory) branches of the autonomic nervous system.
Question 3: During a uterine contraction, blood flow through the uterine spiral arteries temporarily decreases. What is the primary reason for this reduction in flow?
- Maternal Valsalva maneuver during pushing
- Fetal head compression against the cervix
- Increased intramyometrial pressure compressing the vessels (Correct answer)
- Maternal anxiety causing systemic vasoconstriction
Correct answer: Increased intramyometrial pressure compressing the vessels
Uterine contractions increase the pressure within the myometrium (intramyometrial pressure). This increased pressure compresses the spiral arteries that perfuse the intervillous space of the placenta. When the intramyometrial pressure exceeds the pressure within the arteries, blood flow is significantly reduced or even temporarily stopped, leading to a transient decrease in oxygen transfer to the fetus.
Question 4: Fetal baroreceptors, located in the aortic arch and carotid sinuses, are stimulated by changes in fetal blood pressure. What is the expected fetal heart rate response to a sudden increase in fetal arterial pressure?
- An increase in the FHR baseline
- A decrease in FHR variability
- A rapid slowing of the Fetal Heart Rate (Correct answer)
- The development of an acceleration
Correct answer: A rapid slowing of the Fetal Heart Rate
Baroreceptors are stretch receptors that respond to changes in blood pressure. An increase in fetal arterial pressure stretches these receptors, which then send signals via the vagus nerve to the fetal brain's cardioinhibitory center. This results in a rapid, reflexive slowing of the fetal heart rate as a compensatory mechanism.
Question 5: Which of the following components of the maternal-fetal unit carries the most oxygenated blood?
- Maternal uterine artery
- Fetal umbilical artery
- Maternal uterine vein
- Fetal umbilical vein (Correct answer)
Correct answer: Fetal umbilical vein
The fetal umbilical vein is responsible for carrying oxygenated and nutrient-rich blood from the placenta to the fetus. In contrast, the fetal umbilical arteries carry deoxygenated blood and waste products away from the fetus to the placenta. The maternal uterine artery brings oxygenated blood to the placenta, but the exchange process means the blood in the umbilical vein, post-oxygenation, is the most oxygen-rich blood destined for the fetus.
Question 6: A patient is in the second stage of labor, and the fetal monitor shows recurrent early decelerations. This pattern is most commonly associated with which physiological event?
- Umbilical cord compression
- Uteroplacental insufficiency
- Fetal head compression (Correct answer)
- Fetal metabolic acidosis
Correct answer: Fetal head compression
Early decelerations are benign patterns caused by a vagal response to fetal head compression as the fetus descends through the birth canal. The pressure on the fetal skull alters cerebral blood flow, stimulating the vagus nerve and causing a gradual, uniform slowing of the heart rate that mirrors the contraction. The onset, nadir, and recovery of the deceleration coincide with the beginning, peak, and end of the contraction, respectively.
EFM - Electronic Fetal Monitoring Maternal-Fetal Physiology Questions and Answers
A laboring patient who received an epidural anesthetic rapidly develops hypotension.
Which of the following fetal heart rate patterns is most likely to be observed as a direct result of this maternal change?