Why is cst test important

Your baby will be monitored for about 20 minutes, to make sure he's okay. Then you'll be given a small dose of synthetic oxytocin Pitocin in an IV to stimulate contractions. Stimulating your nipples can release natural oxytocin, but this is not as easily controlled as the medication. The contraction test lasts until you've had three contractions in a ten-minute period, each lasting 40 to 60 seconds. This can take up to two hours. You may barely feel the contractions, or they may feel a bit like menstrual cramps; they shouldn't be strong enough to induce labor.

When the test is over, you'll need to stick around until your contractions stop or go back to their pretest level. A negative result If your baby's heartbeat doesn't slow down in response to your contractions, he's probably doing fine. A positive result If your baby's heart beats more slowly after more than half of your contractions, the test result is positive, signaling that your baby may be under stress and unable to tolerate labor contractions.

Equivocal results This might mean that your baby's heart reacted with more frequent or longer-lasting contractions, or that it slowed intermittently.

Learn more : Third trimester prenatal visits What it feels like to have high-risk pregnancy tests The ultimate pregnancy to-do list: Third trimester Pregnancy shopping checklist: Third trimester. Sources BabyCenter's editorial team is committed to providing the most helpful and trustworthy pregnancy and parenting information in the world. Featured video.

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If you don't have a second contraction within 2 minutes of the first, you will rub your nipple again. If contractions do not occur within 15 minutes, you will massage both nipples. After the test, you will be watched until your contractions stop or slow down to what they were before the test. You may need to lie on your left side for the test. This position may not be comfortable when you are having labor contractions.

The belts holding the sensors may bother you. Most women say this test is uncomfortable but not painful. Fetal heart monitoring may show that your baby is having problems when your baby is healthy.

It can't find every type of problem, such as a birth defect. Results of the test tell your baby's health for 1 week. The test may need to be done more than once during your pregnancy. Your baby's heart rate does not get slower decelerate and stay slow after the contraction late decelerations. Note : There may be a few times during the test when your baby's heart rate slows down. But if it doesn't stay slow, it isn't a problem.

Your baby is expected to be able to handle the stress of labor if there are no late decelerations in your baby's heart rate during three contractions in a minute period.

Your baby's heart rate gets slower decelerates and stays slow after the contraction late decelerations. This happens on more than half of the contractions. A contraction stress test may show that your baby's heart rate slows down decelerates when your baby is not actually having problems. This is called a false-positive result. Author: Healthwise Staff. This information does not replace the advice of a doctor. Healthwise, Incorporated, disclaims any warranty or liability for your use of this information.

Your use of this information means that you agree to the Terms of Use. While a nonstress test can offer reassurance about your baby's health, it can cause anxiety, too.

A nonstress test might suggest that a problem exists when there is none, which can lead to further testing. Reassuring results also aren't predictive of the future. Also, keep in mind that while a nonstress test is often recommended when there's an increased risk of pregnancy loss, it's not always clear if the test is helpful. During the nonstress test, you'll lie on a reclining chair. You'll have your blood pressure taken at regular intervals during the test.

Your health care provider or a member of your health care team will place a sensor around your abdomen that measures the fetal heart rate. Typically, a nonstress test lasts 20 minutes. However, if your baby is inactive or asleep, you might need to extend the test for another 20 minutes — with the expectation that your baby will become active — to ensure accurate results.

Your health care provider might try to stimulate the baby by placing a noise-making device on your abdomen. After the nonstress test is complete, your health care provider will likely discuss the results with you right away. A reactive nonstress test is considered reassuring regardless of the length of observation time needed. However, if the test is extended to 40 minutes and your baby's nonstress test results are nonreactive, your health care provider will likely do another prenatal test to further check your baby's health.

For example:. The concept of using FHR patterns to evaluate the fetus and fetoplacental unit is derived from earlier observations made during the intrapartum period. However, it should be clearly understood that observations based on the function of a single system have both diagnostic and prognostic limitations.

Investigators and practitioners have tended to place increasing emphasis on the importance of individual tests, 3 , 4 while occasionally ignoring more global elements of pregnancy. FHR testing must be considered an ancillary aid in clinical decision making and not an ultimate answer to the complex clinical problems faced by obstetricians charged with the care of potentially compromised infants. Heart rate patterns of normal fetuses reflect physiological responses to various endogenous and exogenous stimuli.

Control of FHR requires electrical conduction pathways, cellular receptors to circulating neurohormones, reflex arcs, and inherent myocardial contractility. These components include baseline rate, rate variation, and episodic rate responses to fetal movements accelerations or uterine contractions decelerations. The characteristics of these FHR components are determined by both cellular and systemic mechanisms. The functional units of the fetal heart are myocardial fibers that act as a syncytium; they are endowed with inherent rhythmicity, apparent from the first trimester onward.

Cell growth or hypertrophy is a dominant feature of cardiac development in the final trimester of pregnancy, during which most FHR testing is performed. This process is energy consuming and requires adequate transport of oxygen, glucose, and amino acids. Under normal conditions, the placenta serves as a respiratory and nutritive organ. Nutritive functions, maintained throughout pregnancy, lead to a positive balance of glucose.

Eventual glycogen deposition in cardiac and hepatic tissue provides a reservoir for the stresses of parturition and early neonatal life. Under adverse circumstances e. Placental respiratory failure may alter cellular metabolism.

Increased tissue extraction of oxygen from high-affinity fetal hemoglobin may offer short-term protection from this problem. However, the inability of the placenta to exchange oxygen and carbon dioxide results in fetal respiratory acidosis.

Excess hydrogen ions accumulate in fetal circulation; progressive cellular hypoxia and diminished aerobic metabolism result in development of a secondary metabolic acidosis. Critical intracellular enzymatic reactions begin to fail, and glucose is broken down to lactate and pyruvate, augmenting metabolic acidosis.

Failure to interrupt this sequence of events may lead to cellular death, reduced myocardial contractility, and inability to maintain systemic homeostasis.

The relationship of cellular events to the pathophysiology of FHR tracings is summarized in Figure 1. Although there is controversy regarding the earliest FHR manifestations of cellular hypoxia and tissue acidosis, their expression will depend on both the chronicity and severity of the actual insults and may not be uniformly appreciated by all compromised fetuses.

The ultimate or preterminal patterns associated with cellular hypoxia and systemic asphyxia consist in relatively fixed FHR baselines, reduced or absent FHR variation, absence of FHR accelerations, and the appearance of spontaneous late FHR decelerations. Cellular events and FHR consequences. Unstressed or resting FHR tracings are indices of the following: 1 parasympathetic vagal tone; 2 sensitivity to sympathetic adrenergic discharge; 3 organization of fetal activity or behavioral states; 4 circadian rhythms; 5 the linkage between body movements and accelerations; 6 increasing stroke volume with reduction in resting or intrinsic rate; and 7 integration of reflex responses to momentary fluctuations in arterial blood pressure and gas partial pressures.

These complex interrelationships Fig. FHR accelerative responses are regulated through accelerator nerve fibers arising in the upper thoracic roots and are fine-tuned in the hypothalamic and medullary regions of the brain, which are sensitive to momentary changes in oxygen tension, acid-base balance, circulating catecholamines, and endorphins.

These pathways are evident as early as the midtrimester. Factors influencing generation of FHR pattern. Fetal movements become increasingly frequent in the midtrimester and act as triggers for transient baseline alterations with stronger linkages as term is approached.

Others 11 , 12 have reported that the frequency of movement-associated decelerations decreases with gestational age, especially after 29—32 weeks. Behavioral organization becomes more important in the late third trimester, since clustering of movements and accelerations become more apparent during this general time frame. The element of time plays a greater role in the occurrence of FHR patterns as fetal cardiovascular control systems mature. Nonrandom, periodic cycles of FHR are generated, lasting from 60 to minutes, 16 with a mean duration of approximately 90 minutes at term.

As state organization becomes better defined, epochs of low variability and decreased movement incidence recur, lasting as long as 90— minutes, with a mean of approximately 20 minutes. Diurnal fluctuations in body movements have been reported, with peaks occurring between and hours. Maternal factors may influence the patterns present in resting FHR tracings.

Maternal fed state, responsible for maternal glycemia, has had an inconsistent effect on reported FHR responses. Maternal activity levels 22 are also associated with a variety of FHR patterns. Normal ambulation 23 appears to have little appreciable influence on either subsequent baseline rate or acceleration incidence; graded vigorous exercise may cause transient but unpredictable tachycardias and bradycardias. Systemic influences on resting FHR tracings due to ongoing maternal or fetoplacental pathology have a common pathway in which oxygenation and energy substrates are reduced.

In the absence of acidosis, acute disturbances of placental respiratory or nutritive function may result in sudden and profound decrease in fetal movement incidence. The corollary to this situation would be marked decreases in acceleration frequency.

More commonly, diminished placental functions are more subtle, tend to be chronic, and lead to gradual declines in fetal movement incidence and acceleration frequencies as compensatory visceral shunting of the fetal circulation occurs. As term pregnancy approaches, the frequency of spontaneous uterine activity increases and individual contractions tend to become longer and more intense.

Early data, using direct measurements of intrauterine pressure, suggest that a contraction intensity of more than 35 mmHg is needed before the effects of transient hypoxia are consistently appreciated by borderline or compromised fetuses. During any given contraction of moderate to strong intensity, intervillous space blood flow is greatly reduced or abolished, restricting oxygenation of the fetus. The hypoxemic fetus tolerates such stress poorly, and myocardial homeostasis becomes insufficient to maintain effective cardiac output during this period.

The resulting late FHR decelerations have both a reflex component i. It should be carefully noted that other mechanisms may be responsible for late FHR decelerations: 1 intrinsic maternal hypoxemia respiratory disease, anemia ; 2 maternal hypotension aortocaval compression, drugs ; or 3 compromise of umbilical venous blood flow partial cord occlusion.

Basal fetal oxygenation. The relationship of late decelerations to baseline fetal oxygenation during contractions. Uterine activity may also be associated with fetal movements and FHR accelerations. Therefore, this clinical correlation should be interpreted cautiously during antepartum monitoring. Subsequently, more than studies of the NST have appeared in English language literature and numerous approaches for using this test have been evaluated. Most NST schemes use minimum thresholds of FHR acceleration frequency to distinguish healthy from compromised fetuses.

Most obstetric laboratories now use FHR transducers operating in either continuous or pulsed Doppler modes rather than phonocardiographic or abdominal electrocardiographic signal sources. Advances in Doppler signal processing, using onboard autocorrelation techniques, 41 , 42 have produced legible FHR tracings that appear similar to those obtained from direct fetal scalp electrode sources.

However, external FHR signals generated in this manner do not represent true electrocardiographic R-R intervals. External tokodynamometer devices are used to register uterine activity. These transducers are sensitive to changes in surface abdominal wall tension, and their reliability and relationship to actual intrauterine pressure readings have been well studied. The validity of using patient-operated markers for fetal activity is dependent on the quality of patient involvement and education, and corroboration by experienced observers.

Points to be emphasized during performance of the NST include uniformity of testing conditions, length of observation, consideration of maternal status, and selection of high-fidelity recording equipment. Fetuses are often tested on more than one occasion, emphasizing the need for careful control of such factors as time of day, maternal activity levels, medication and dietary status, and observation techniques if serial comparisons of tests are to be considered in management protocols.

Although no minimum length of testing has been universally accepted, extremely short intervals 10 minutes or less may result in interpretative and classification errors for normal fetuses. Maternal positioning should prevent aortocaval compression, vital signs should be recorded every 10—15 minutes, and any unusual events such as audible FHR irregularities should be noted. Finally, the quality of recorded signals is a limiting factor for interpretation. It is of paramount importance if the NST is to be a useful screening or diagnostic test.

Fortunately, most current operating systems are capable of achieving excellent-quality tracings, have wide-range probes, and are relatively tolerant of shifts in fetal position. The testing protocol used at the Medical College of Georgia is outlined in Table 1. Earlier approaches had advocated manual palpation or shaking of the fetal head or body.

However, these maneuvers have not consistently elicited more frequent accelerations or led to shorter testing times. Initial studies used pure tone generators.

This device produces a broadband acoustic signal and a complex vibratory component. The stimulator is applied to the maternal abdomen in the region of the fetal head, then a 3-second pulse is delivered. A sample VAS-evoked reactive test is shown in Figure 4. The rapid appearance of a FHR baseline elevation that follows is a typical response to this maneuver. The most significant factor that influences fetal response to VAS appears to be gestational age.

Gagnon and co-workers 50 showed that, as the fetus matures, there is increased consistency of response to VAS, in terms of increased body and breathing movements, suggesting that this stimulus may produce a change in organized fetal behavioral state.

Subsequently, Devoe and colleagues 51 confirmed with real-time ultrasound and simultaneous FHR recordings that behavioral states may be altered by VAS, primarily when fetuses are in quiet sleep state 1F. In an additional study, 52 this group quantitated the typical responses of healthy term fetuses to VAS. Their data showed that nearly all such fetuses will respond to a standard stimulus with at least a 10 bpm rise in baseline, occurring in about 7—10 seconds and lasting from 5—10 minutes.

While VAS promises to effect a test with similar predictive value in a potentially shorter time frame, there has been concern about its safety and long-term sequelae. Unfortunately, there are few direct data to address these issues. In utero sound pressure levels have been measured with specially adapted hydrophones, yielding stimulus peaks ranging from 98 to db. Adaptations of Doppler signal processing enabled the development of a method of antepartum monitoring which combines the simultaneous detection of FHR and fetal body movements.

This approach takes advantage of special band-pass filters which, when applied to the raw Doppler signal, allow isolation of the low frequency shifts associated with fetal movement from the higher frequency alterations associated with fetal cardiac motion.

A number of groups have developed monitoring systems that display these data simultaneously 55 , 56 Fig. A fetal actocardiograph with automatic indication of fetal movements dark horizontal bars on second channel. Note their concordance with FHR accelerations and maternal perceptions light vertical bars. Stanco and co-workers 59 showed that the use of actocardiography in antepartum testing decreased significantly 5. A large survey of actocardiography compared the predictive values of Doppler movement detection with standard reactivity parameters of the NST.

Application of actocardiography to actual fetal assessment should still be considered investigational. The additional data obtained from detecting fetal movements would appear to aid in the distinction of true and false nonreactive tests, and help to distinguish changes in fetal behavioral state.