The maternity nurse understands that vascular volume increases 40% to 45% during pregnancy to:

Choice A reason: Vibroacoustic stimulation is a technique that uses sound to stimulate the fetus and elicit a response. It is sometimes used in conjunction with the nonstress test (NST), not the CST. The NST measures the fetal heart rate (FHR) in response to fetal movement, while the CST measures the FHR in response to uterine contractions.

Choice B reason: A negative CST result means that the FHR does not show any late decelerations during at least three contractions in a 10-minute period. Late decelerations are decreases in the FHR that begin after the peak of a contraction and return to the baseline after the contraction ends. They indicate uteroplacental insufficiency, which means that the placenta is not delivering enough oxygen and nutrients to the fetus. A negative CST result is reassuring and suggests that the fetus is well-oxygenated and can tolerate labor².

Choice C reason: The CST is not an invasive test, as it does not involve inserting any instruments or devices into the uterus or the fetus. However, it does require stimulating contractions, either by giving the pregnant woman oxytocin (a hormone that causes uterine contractions) or by having her rub her nipples (which also releases oxytocin). The contractions can be uncomfortable and may trigger preterm labor in some cases.

Choice D reason: The CST is not more effective than the NST if the membranes have already been ruptured. In fact, the CST is contraindicated (not recommended) in women who have ruptured membranes, as it can increase the risk of infection and bleeding. The NST is a safer and simpler alternative to the CST, as it does not require stimulating contractions. However, the NST may not be as reliable as the CST in detecting fetal compromise.

Choice A reason: The NST has no known contraindications, as it is a non-invasive and safe test that does not stimulate uterine contractions or cause fetal distress. It is the most widely used method of antepartum fetal surveillance.

Choice B reason: The NST is not slightly more expensive than the CST, as it requires less time and equipment. The NST usually takes 20 to 40 minutes, while the CST may take up to 2 hours. The NST only needs a fetal monitor, while the CST also needs an intravenous line and oxytocin infusion.

Choice C reason: The NST does not have fewer false-positive results than the CST, as it has a higher rate of nonreactive results that may indicate fetal compromise when there is none. A nonreactive NST is one that does not show at least two accelerations of the fetal heart rate of 15 beats per minute or more lasting 15 seconds or more in a 20-minute period.

Choice D reason: The NST is not more sensitive in detecting fetal compromise than the CST, as it has a lower predictive value for fetal well-being. A reactive NST is one that shows at least two accelerations of the fetal heart rate of 15 beats per minute or more lasting 15 seconds or more in a 20-minute period. However, a reactive NST does not rule out the possibility of fetal hypoxia or acidosis.