Maternal-Fetal Physiology Flashcards

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?

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.

Which physiological mechanism is primarily responsible for the presence of moderate variability in the fetal heart rate?

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.

During a uterine contraction, blood flow through the uterine spiral arteries temporarily decreases. What is the primary reason for this reduction in flow?

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.

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?

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.

Which of the following components of the maternal-fetal unit carries the most oxygenated blood?

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.

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?

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.