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Antenatal Fetal Assessment 

Indications for fetal surveillance. At our testing center we donít look at babies for post date indications until they are 41 weeks or beyond. Normal babies donít have an increased risk of perinatal injury until they are beyond 41 weeks of gestation. In diabetics we start at 36 weeks with class A or type II diabetics. With type I diabetics, the insulin-dependent, prior to the onset of the pregnancy we start testing by 32 weeks of gestation. Hypertensive disease: this is chronic hypertension. Prior still birth 34 weeks or around the time the still birth was diagnosed. Decreased fetal movement and growth restriction needs to be started at the time of those diagnoses antenatal fetal assessment, fetal monitoring, fetal monitors, decelerations, decellerations

So what do we look for when we are looking at the non-stress test? You are trying to see accelerations in fetal movement, which would coincide with response to activity in the fetus. We see accelerations of the heart rate associated with movement. They can be spontaneous also. They are caused by stimulation of the cardiocilitory fibers in the vagal system. And they can be present early in gestation. They are modulated or modified by behavioral states, wake versus sleep cycles, by gestational age. Drugs and other medications that the mother may

Pathophysiology of accelerations. You will see a decrease in the accelerations first by amplitude and frequency. To the babies continue to have accelerations but the peak wonít be as high and they wonít occur as often. So with increasing difficulties in utero youíll see a decreased incidence of movement so the acceleration amplitudes are affected before the fetal movement alters. Then youíll see a de-coupling. That the

Criteria for finding a non-stress test are reactive. Non-stress testing is used because of its ease of availability as well as how easy they are to conduct. You donít have to have IVís in place, you donít have to have anything special be on the monitor and the paper to read the monitor strip on. So you have two accelerations in a ten minute period, or two accelerations in a 20 minute period. Both of these have held the test of time as far as being considered accurate for a 3-4 day period of time. There should be some assessment of variability in association with these accelerations. There are some computerized programs that look at multiple parameters. The majority of that is looking at variability in

The frequency of testing with postdates should be twice a week, with gestational diabetes once a week, and with diabetics twice a week and when they have documented small vessel disease, a prior history of still birth once a week, growth restriction twice a week as well as

Now predictive is a non-stress test, a reactive non-stress test? When we looked at the mortality rate per thousand, and the corrected mortality rates here are corrected for anomalous fetuses. Babies that were born and then found to have significant malformations after birth

Contraction stress testing, or testing of different systems essentially. The non-stress test is testing the vasovagal response to stimulation as seen by fetal movement. The contraction stress test is looking at the fetal response from the standpoint of the uteroplacental unit. So you are looking at how well the uterus is perfused, how much oxygen the placenta is receiving and relaying on to the fetus. Contraction stress testing requires that there is a least three contractions in a ten minute period so it is resembling labor, a far as the kind of stress that will relay to the baby. Those contractions can be obtained spontaneously. If the patient comes in and is contracting that frequently, you can have a spontaneous CST. Nipple stimulation is another way to achieve three contractions in ten minutes, then IV oxytocin. The only caveat to nipple stimulation is that it is a non-controlled form of oxytocin release and you can get some pretty significant releases depending on how vigorous the stimulation is, how much that person tends to respond to that nipple stimulation, so you can get some hyperstimulation in that instance. When you look at the contraction stress test, the negative test is where you see no decelerations so the best thing you will see - if you use NST and CST together, is a reactive NST and a negative CST. Contraction stress tests are considered positive if you see late decelerations

An equivocal stress test is a test that either has non-repetitive late deceleration and many authors will also throw in that they have decelerations that are not late in nature, such as variable decelerations especially if there are severe variables. Hyperstimulation may occur and you almost have to write that test off as being something that is no interpretable if you have hyperstimulation of the uterus.

There are some contraindications. Unlike non-stress testing there are contraindications to doing contraction stress testing. You shouldnít do it in the presence of a placenta previa. Essentially these are things that are contraindications to labor. Previous classical cesarean section,

A negative CST really is indicative of fetal well-being for seven days in the majority of patients. A positive CST, you need to evaluate those fetuses for delivery. That doesnít mean that these patients need to be evaluated for immediate cesarean section. Our rationale here is if we have to do a contraction stress test on someone and decide that it is positive, their cervix is evaluated and usually we just leave the oxytocin running, if we are doing it with IV oxytocin, to try to stimulate labor and make a decision based on optimal hydration, positioning of the

There are some reversible causes for having an abnormal contraction stress test. The number one thing that most of them deal with maternal physiology and why the mother may be hypoxic or acidotic. Diuretic induced acidoses. Acidoses will frequently be also manifested by preterm contractions because of the volume contracted state these patients are in. So you frequently see spontaneous contraction stress tests with what appears to be a poorly oxygenated fetus. You very seldom see that maternal ketoacidosis will result in the resolution of the fetal heart rate tracing.

Sickle-cell crisis and other anemiaís will result in hypoxia to the fetus and uterus and result in abnormal contraction stress testing. Asthma, especially if itís manifested by maternal hypoxia and acidosis and significant dehydration are al reversible causes. Now what we tend to use here almost exclusively is a combination of a non-stress test with amniotic fluid index. Or some form of assessment of amniotic fluid. Iím

Amniotic fluid index divides the uterus into four quadrants with the umbilicus and the linea nigra serving as the landmarks to split into those four quadrants. You keep the transducer of the ultrasound perpendicular to the floor and measure the largest vertical pocket of fluid in each quadrant. You sum that up to get your amniotic fluid index. Itís normal if itís greater than 8, intermediate between 5-8, and oligohydramnios is diagnosed for those less that 5. The upper limit of normal here is 25 centimeters in a singleton pregnancy. This is just one of the 

This is the inter-observer error. One centimeter versus two centimeters difference with an AFI of less than 20 and the inter-observer error is very similar, so they are pretty close.

Management of the oligohydramnios I think in our department had been very controversial for a period of time. I think itís becoming more and more accepted that, especially at term, oligohydramnios needs to be respected as a chronic marker for something going on with that fetus or with the uteroplacental unit. If the baby is term and you know that you have pulmonary maturation you should consider delivery for these patients. In the preterm infant with a diagnosis of oligohydramnios you need to do an anatomic survey of the baby looking for any abnormalities. Consideration for prolonged or even hospitalized monitoring for these fetuses and evaluation for premature rupture of membranes. And consideration for additional surveillance techniques, including Doppler which I will discuss in a little while. You need to consider that these babies are at risk for pulmonary hypoplasia and that delivery of these infants may result in a pulmonary death shortly after birth. And then continue with an ultrasound evaluation for growth assessment to make sure that these babies are normally grown. You see a

Again, post-dates we test twice weekly and start that at 41 weeks of gestation. We consider babies candidates for delivery if they have very low decelerations on their non-stress test or have decreases in AFI. With growth restriction babies I think that _ babies should have, if thatís the reason why you are testing them and an amniotic fluid index should be added because of their risks of chronic oligohydramnios with

With premature rupture membranes there is a controversy over the role of daily testing within these fetuses. We probably monitor them here too much. They usually on twice-daily testing while they are here because they are hospitalized and it just keeps everybody from worrying about them as much, I think. But you need to consider some kind of, at least consistent testing for these babies. And have parameters for when you would stop. If you are going to test them twice a week, which I think is reasonable in a normally grown fetus, you have to make

Biophysical profile is described by Manning. There are five things that you need to look at. The first one is non-stress testing and if your non-stress test is reactive you get a score of 2 for that. The second one is normal amniotic fluid index. The normal parameter would be greater than 8 with a score of 2 for that if you use the index. A pocket of at least 2 centimeters You want to see fetal breathing. So the

When you look at the management of a biophysical profile, scores of 8 and 10 so usually things that patients get points off for - the first one that usually goes is the non-stress test. And what we do is we do a non-stress test and if thatís abnormal we look at fluid. And if the non-stress test and the AFI are abnormal we will complete the rest of the biophysical profile. So we use the biophysical profile in conjunction

Now the 1% incidence of false negatives: babies who have a normal test but have an intrauterine death. This is a list of the things that we consider most likely to have caused false negative testing. A cord accident, either a cord prolapse or a cord entanglement. Undiagnosed oligohydramnios, if you are just doing non-stress testing. An acute metabolic disorder such as an asthma attack, diabetic ketoacidosis. An

When you look at decelerations during the non-stress test you need to consider abnormal abnormalities and cord position, either phrenic presentation - the cord is above the head - you have nuchal cord - that itís entangled in the legs - oligohydramnios, fetal anemiaís. Ultrasound is often helpful in trying to delineate what may be wrong, especially when you look at the two most common things you could evaluate by ultrasound to some degree. And even more in post date babies we see this frequently in babies who, once amniotomy has been performed, have meconium staining of 

Why do babies have a false positive test, a non-reactive test if they are normal? Prematurity is probably the most common thing we deal with. Some babies, even though we anticipate the majority of the non-stress testing is going to be reactive in a normal fetus, by 28 weeks of gestation some of these babies wonít mature enough to respond to motion normally until they are 32 weeks. So maybe a response of

When you look at the heart rate testing of the premature baby youíve got to realize that you are going to have to do something more liberal and we liberally use biophysical profile testing for these babies. You can start non-stress testing as early as 25 weeks. The summary liability of its predictability of 

Now the amniotic fluid, just briefly, one of the things that you need to keep in mind is that there is a 95% turnover every day. In the second and third trimester the fetus has a large role in maintaining its own amniotic fluid environment where prior to the second trimester this is all pretty much an osmatic phenomenon.

Some of the things about prematurity and fetal heart rate testing that are significant: youíll see higher base lines with heart rate testing in the premature infants, fewer reactive patterns or youíll see accelerations but with decreased amplitude. These babies, when you use acoustic

Cases that are at risk for having abnormalities in their amniotic fluid index or their amniotic volume: Post dates, growth restriction, diabetes mellitus. These two usually we are seeing decreased amounts of fluid, diabetes in the uncontrolled diabetic who doesnít have small vessel disease, this is often manifested by polyhydramnios. When you have small vessel disease then the babies have an increased risk of growth restriction and youíll see oligohydramnios in those patients. Sometimes with even extremely poor blood sugar control. Isoimmunization is another polyhydramnios phenomenon. You will see elevations of the amniotic fluid index in babies whose mothers have Rh isoimmunization or other red cell antibodies that result in fetal anemia. Twin gestations, especially when you have monochorionic twins where twin to twin transfusion syndrome can ensue and you get polyhydramnios-oligohydramnios syndrome or Stuckís twin syndrome, and then anything that causes non-immune hydrops: cystic hygromas, congestive heart failure from congenital heart block. Those babies will manifest with polyhydramnios when they non-immune hydrops.

Babies with intrauterine growth restriction are probably one of the most common things we deal with as far as the frequency of testing and the onset of early testing. Usually we use the non-stress test, the amniotic fluid index in conjunction here with the SD ratio or the Doppler velocimetry to assess these fetuses. Doppler velocimetry, when I explain it to patients I try to explain to them that this is sort of analogous to

In babies who have normal heart rates and normal AFIís but have markedly elevated SD ratios, there are some authors who would advocate testing these babies on a daily basis. Probably no less than twice a week should these fetuses be tested. I think it depends on if this is an

Some of the indications for Doppler velocimetry evaluations: itís probably much more limited than the indications for non-stress testing or biophysical profile testing. The only thing that has been proven to be predictive of fetal death - and you can use it to decide whether or not a baby should be delivered - is with absent or reverse end diastolic flow in the growth restrictive baby, it is very predictive of perinatal death. When I talk to patients about something being very predictive of perinatal death, unfortunately what I am telling the parents and have to explain to them in detail is that something is going on with this baby that is so severe then when we deliver the baby we may nor impact on its ability to survive. Based on gestational age, but also because of whatís going on. Babies with severe IUGR and abnormalities in Doppler velocimetry that are manifested by reverse flow have a very high newborn mortality rate also. So delivery may not be the answer for these babies. When you see discordant growth in twins there may be a role for Doppler velocimetry. There have been some people advocating it

The placenta is a high flow low resistance blood flow system in the majority of cases. And how low that resistance is correlates very well with the ability of the fetus to grow in utero. This looks at gestational ages and weights based on what the Doppler velocimetry showed. With SD ratios less than 3, babies usually deliver at term and with normal birth weights. Or if you had absent diastolic flow they were delivered

Doppler shifts. The question is what the clinical application of this is. Probably the only clinical application is for growth restricted babies. The more we know about it the more likely thatís the only thing we will be able to use it with.

Hydramnios: hereís a list of things that we know are significant for the onset of hydramnios or increased amounts of fluids and a list of things that are associated with oligohydramnios and