Ante Part Um Testing

8/2/2019 Ante Part Um Testing

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Antepartum Fetal Monitoring


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To learn a systematic approach for describing and interpreting theresults of the fetal heart rate tracing.

To learn the techniques for performing the components of themodified biophysical profile and the full biophysical profile.

To review the perinatal mortality associated with each of thepossible biophysical profile scores.

To review the association between the presence or absence ofeach of the components of the biophysical profile score andacidosis.

Learn the appropriate response for test results based onprocedures and policy established by your department.

Objectives


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The goal of antepartum fetal surveillance is to preventfetal death.The MBPP is an abbreviated biophysical profile thatincludes only the nonstress test (NST) and amniotic

fluid index (AFI). A normal result is a reactive NST withan AFI > 5.0 cm.In one series the stillbirth rate, corrected for lethalcongenital anomalies and unpredictable causes ofdemise was 0.8 per 1,000 in 54,617 modified BPPs,

and the negative predictive value of the modified BPPwas greater than 99.9%.

Antepartum Fetal Surveillance


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The nonstress test (NST) is performed byauscultation of the fetal heart rate using anelectronic monitor.

The Nonstress Test


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The Nonstress Test

The ultrasound probe transmits the

fetal heart rate in beats per minute.

Each small vertical square is 10beats.

Each small horizontal square is 10seconds .

Each large horizontal square is 1minute .

The pressure transducer

transmits the pressure generated

by uterine contractions in mm Hg.

Each small vertical square is 5 mmHg

Each small horizontal square is 10seconds .

Each large horizontal square is 1minute .Pressure Transducer

Ultrasound Probe


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The interpretation of the fetal heart rate tracing shouldfollow a systematic approach with a full qualitative andquantitative description of the following:

Baseline rateBaseline fetal heart rate (FHR) variabilityPresence of accelerationsPeriodic or episodic decelerationsChanges or trends of FHR patterns over timeFrequency and intensity of uterine contractions

Interpretation of the Fetal Heart Tracing


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The baseline FHR is the heart rate during a 10minute segment rounded to the nearest 5 beat perminute increment excluding periods of marked FHRvariability, periodic or episodic changes, and segments

of baseline that differ by more than 25 beats perminute.

The minimum baseline duration must be at least 2minutes. If minimum baseline duration is < 2 minutes thenthe baseline is indeterminate.

Baseline Fetal Heart Rate


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Two Minutes


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Baseline change:The decrease or increase in heart rate lasts for longerthan 10 minutes.


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Bradycardia

Mean FHR < 110 BPMA rate of 100-119 BPM in the absence of other nonreassuring patterns is not usually a sign of compromise

CausesHeart block (little or no variability)Occiput posterior or transverse position

Serious fetal compromise.

Patients with new onset bradycardia should betransferred to Labor and Delivery for furtherobservation and physician notified


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Tachycardia

Mean FHR>160 BPMIn the presence of good variability tachycardia is not asign of fetal distress

Causes:Maternal feverFetal hypoxiaFetal anemiaAmnionitis

Normal variantFetal tachyarrhythmia(usually > 200 BPM withabrupt onset little to novariability)

SVT (200-240 BPM)Fetal heart failureDrugs

Beta sympathomimetics

Vistaril

PhenothiazinesRebound transient tachycardia

following a decelerationaccompanied by decreasedvariability)


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Tachycardia


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FHR Variability

Fluctuation in baseline FHR > 2 cycles per minute.

No distinction is made between short-term variability (orbeat-to-beat variability or R-R wave period differences in

the electrocardiogram) and long-term variability.


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Development of FHR Variability

Early in gestation the fetal heart rate is predominatelyunder the control of the sympathetic nervous systemand arterial chemoreceptors.

As the fetus develops its heart rate decreases inresponse to parasympathetic (vagal stimulation)nervous system maturation and variability becomesmore pronounced.


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FHR Variability

Grades of fluctuation arebased on amplitude range(peak to trough)

A sinusoidal pattern hasregular amplitude and

frequency and isexcluded in the definitionof variability.

The tracing to the rightshows an amplitude rangeof ~ 10 BPM (moderatevariability).


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FHR Variability

Absent variability =Amplitude range undetectable

Minimal = < 5 BPM

Moderate = 6 to 25 BPM

Marked = > 25 BPM


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How Hypoxia (Low Oxygen) Leads toAcidosis and Decreased FHR Variability

The fetus uses oxygen to "burn" molecules andrelease energy.

The reaction: glucose + oxygen >> carbon dioxide +

water + energy

Poor blood flow from the uterus and placenta causesthe fetus to constrict blood vessels in nonvitalperipheral areas such as the arms and legs in order to

supply more blood flow to vital organs such as theheart and brain.


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How Hypoxia (Low Oxygen) Leads toAcidosis and Decreased FHR Variability

With a limited supplies of oxygen (hypoxia) theperipheral tissues can only partially break down thesugar and converts it to lactic acid.

Significant levels of acid in the blood (acidemia) maysuppress the fetal nervous system and eventually lead

to cardiovascular collapse.


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The Presence of Moderate FHR Variability isReassuring .

Persistently minimal or absent FHR variabilityappears to be the most significant intrapartum sign offetal compromise.

On the other hand the presence of good FHR variabilitymay not always be predictive of a good outcome (such asmay occur with an abruption).


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Fetal metabolicacidosis

CNS depressants

Fetal sleep cycles

Congenital anomalies

Prematurity

Causes of Decreased Variability

Fetal tachycardiaPreexisting neurologicabnormalityNormal variantBetamethasone


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Sinusoidal and Pseudosinusoidal Patterns

Sinusoidal pattern:A smooth, undulating pattern,lasting at least 10 minutes with afixed period of three to fivecycles per minute and anamplitude of 5-15 bpm.

Pseudosinusoidal:Usually caused by drugs such

as Nubain or Stadol.


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An acceleration is an abrupt increase in FHR above baseline withonset to peak of the acceleration less than < 30 seconds andless than 2 minutes in duration. The duration of theacceleration is defined as the time from the initial change inheart rate from the baseline to the time of return to the FHR tobaseline.

15 BPM above baseline for > 15 seconds[3].

Prolonged acceleration: Increase in heart rate lasts for 2 to10 minutes.

The absence of accelerations for more than 80 minutescorrelates with increased neonatal morbidity.

Accelerations


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A NST is considered reactivewhen two or more fetal heartrate accelerations peak (but donot necessarily remain) at least

15 beats per minute abovethe baseline and last 15seconds from baseline tobaseline within a 20 minuteperiod with or

without fetal movementdiscernible by the woman.

Reactivity


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If the pattern is nonreactive after 20 minutes ofobservation then vibroacoustic stimulation(VAS), using an artificial larynx, may beperformed.

The acoustic stimulator should be positioned on thematernal abdomen and a stimulus of 3 seconds orless applied near the fetal head. If the NST remainsnonreactive, the stimulus is repeated at 1-minute

intervals up to three times.

Vibroacoustic stimulation (VAS)


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A reactive NST has been associated with aperinatal mortality of approximately 5/1,000.

The false-positive rate (the test indicates fetalcompromise when the fetus is actually O.K.)associated with the nonreactive NST isapproximately 75 to 90 percent

Malformed fetuses have a higher incidence ofnonreactive NSTs.

How Reassuring is a Reactive NST?


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A nonreactive NST is one that lacks sufficient fetal heart rateaccelerations as described above over a 40-minute period.

Overall, on initial testing, 85 percent of NSTs will be reactive and15 percent will be nonreactive

Most fetuses exhibiting a nonreactive NST will not becompromised but will simply fail to exhibit heart rate reactivityduring a 40-minute period of testing .

~50 percent of NSTs are nonreactive between 24 and 28 weeks'

gestation.~15 percent of NSTs remain nonreactive between 28 and 32

weeks.

Likelihood of a Nonreactive NST


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A non-reactive NST requires that abiophysical profile be done.


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Episodic patterns are those not associated with uterinecontractions

Periodic patterns are those associated with uterinecontractions.

Early and late decelerations (with some exceptions-i.e., supine hypotension) are periodic.

Variables can also be periodic.

Quantitated by the depth of the nadir in BPM below thebaseline.

Duration is quantitated in minutes and seconds from thebeginning to the end of the deceleration.

(Accelerations are quantitated similarly.)

Periodic or Episodic Decelerations


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The type of the deceleration is distinguished on thebasis of its waveform.

Abrupt (variables) decrease in FHR belowbaseline with onset to nadir < 30 seconds.

Gradual decrease and return to baseline with time

from onset of the deceleration to nadir >30seconds.

Further subclassified based on their relation tothe contraction.

Early decelerations: The nadir occurs withthe peak of a contraction.

Late decelerations:The nadir occurs afterthe peak of a contraction.

Decelerations


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Abrupt decrease in FHR of >15 beats per minute measuredfrom the most recentlydetermined baseline rate. Theonset of deceleration to

nadir is less than 30seconds. The decelerationlasts > 15 seconds and lessthan 2 minutes. A shoulder, ifpresent, is not included as partof the deceleration.

Variable decelerations may beobserved in up to 50% ofNSTs. If nonrecurrent and


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Gradual decrease in FHRwith onset of deceleration

to nadir >30 seconds. Thenadir occurs with the peakof a contraction.

Early Deceleration


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Gradual decrease in FHRwith onset of

deceleration to nadir>30 seconds. The nadirof the deceleration occursafter the peak of thecontraction

Late Deceleration


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These decelerations appear to be mediated byarterial chemo receptors in mild hypoxia.

Below a pO2 of 15-20 mm Hg chemoreceptorsare triggered causing reflex alpha adrenergicstimulation leading to hypertension.

The hypertension stimulates a baroreceptor

mediated vagal response (deceleration) The onset of reflex late decelerations typically

precedes the loss of accelerations

Late Decelerations

Late Decelerations associated with preservation of beat-to beatvariability


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Lates associated with no variability (where loss of variabilityhas not been caused by drug administration)

With progressing hypoxia, the decelerations become deeper.

As acidosis develops the brain stem reflexes become blunted anddirect myocardial depression causes shallow decelerations [20,22].

If myocardial depression is severe enough, lates may be absent alltogether

CAUSES

Excessive uterine contractions (hyperstimulation), maternalhypotension, or maternal hypoxemia.

Reduced placental exchange as in hypertensive disorders,diabetes, IUGR, abruption.

Late Decelerations


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Late Decelerations

From: Sweha A, Hacker TW, Nuovo J. Interpretation of the electronic fetal heart rate during labor.

Am Fam Physician. 1999;59:2487-500


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Late Decelerations

Management

Place patient on side

Administer O2 by tight face mask

Discontinue oxytocin.

Correct any hypotension

IV hydration.

If hyperstimulation is present consider terbutaline 0.25mg SC

If late decelerations persist for more than 30 minutes

despite the above maneuvers, fetal scalp pH is indicated.Scalp pH > 7.25 is reassuring, pH 7.2-7.25 may berepeated in 30 minutes.

Deliver for pH < 7.2 or minimal baseline variabilitywith late or prolonged decelerations and inability toobtain fetal scalp pH

These maneuvers are primarily intended to alleviate "reflex" lates.


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Decelerations occur with > 50% of uterine contractions in any20 minute segment.

Recurrent variable decelerations (at least 3 in 20minutes) may be observed. However, close follow up is

recommended because cord accidents with subsequentfetal death may occur even in the presence of normalamounts of amniotic fluid.

Recurrent late decelerations should lead to considerationof cesarean delivery unless the abnormal results are

believed to be the result of a reversible maternal conditionsuch as diabetic ketoacidosis or pneumonia withhypoxemia.

Recurrent Decelerations


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Maternal hypotension

Uterine hyperactivity

Cord prolapse

Cord compression*

Prolonged Decelerations

A decrease in FHR of > 15 beats per minute measured fromthe most recently determined baseline rate. The

deceleration lasts >= 2 minutes but less than 10 minutes.

Causes:

Rapid descent of fetal head

Abruption

Artifact (maternal heart rate

Maternal seizure


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Prolonged Decelerations

Patients with a fall in the fetal hear rate of 15 PBMbelow the baseline for 1 minute or longer should

be considered for transfer to Labor and Deliveryfor further observation and physician notified


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The Contraction Stress Test (CST)

The Contraction stress test is used by some antepartumtesting centers to evaluate placental function under stress.The test is performed by placing transducers (ultrasound andtoco), on patient's abdomen as with the nonstress test.

The tracing is then observed for late decelerations.

The test requires three contractions in 10 minutes to bepresent with the contractions lasting 40 to 60 seconds.

If uterine activity is absent then oxytocin is infused or nipplestimulation is used.


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The test is positive if late decelerations areconsistent and present with more than 50% of thecontractions.

A positive CST has been has been associated with

an increased incidence of intrauterine death, latedecelerations in labor, low 5-minute Apgar scores,and intrauterine growth restriction.

The CST is equivocal or suspicious if there areintermittent late decelerations


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Although the CST is not used routinely by the SanGabriel Valley Perinatal Medical Group a fetaltracing may fulfill the requirements for a positiveor suspicious CST spontaneously.

A suspicious or equivocal CST should berepeated in 24 hours


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Amniotic Fluid Index (AFI)

The amniotic fluid index is

measured by dividing theuterus into four quadrants

The linea nigra is used todivide the uterus into rightand left halves.

The umbilicus serves as thedividing point for the upperand lower halves.

The transducer is keptparallel to patients

longitudinal axis andperpendicular to the floor.


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Amniotic Fluid Index (AFI)

The deepest, unobstructed,vertical pocket of fluid ismeasured in each quadrant

Brief appearances of cord or

an extremity are ignored, butaggregation of either one, tothe exclusion of fluid, is notconsidered part of a fluidpocket.

Add these numbers togetherand the sum represents theAmniotic fluid Index (AFI).


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Interpretation of the AFl

10.1 to 24.0 cm Normal5.1 to 10.0 cm Borderline

Less than or equal 5.0 cm AbnormalGreater than 24.0 cm Abnormal


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Risk of Oligohydramnios after "Low-normal AFI"

Gestational Age(weeks) AFI Risk of Oligohydramniosafter 4 days>41 5-8 23.3%

37-40 5-8 17.8%>41 >8 7.4%

37-40 >8 3.7%


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Abnormal AFI Results

Notify attending physician for possible evaluation offunctioning renal tissue and intact membranes for AFIless than or equal to 5.0.

Notify attending physician for possible evaluation of fetalstructural abnormalities or diabetes for AFI greaterthan 24

Patients with an AFI less than or equal to 5.0 shouldbe transferred to Labor and Delivery for furtherobservation and physician notified


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The Biophysical Profile (BPP)

Between 24 and 28 weeks' gestation, approximately50 percent of NSTs are nonreactive.

In contrast sonographically evaluated variables arevalid early in gestation and account for three of thefive components of the biophysical profile.

The biophysical profile may be used to verify fetal

well being when the nonstress test is not reactive.


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Fetal movement and fetal tone develop between 7.5and 9 weeks menstrual age.

Fetal breathing movements are detectable by, at least

17-18 weeks gestation.

Amniotic fluid may be reduced as early as 17.5 weeksby fetal acidosis.

The components of the biophysical profile developsequentially. In order of appearance: tone, movement,breathing, reactivity.


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Fetal state (wake-sleep cycle) plays an important

role in the interpretation of the biophysical profilescore.

In quiet sleep the average time to obtain a normalbiophysical profile score is 26.3 minutes.

The biophysical profile score is, therefore, continuedfor a maximum of 30 minutes.


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The sonographic variables that develop lastin gestation are the most sensitive to acidosisand would be the first components of the BPP

to become abnormal.

The NST, breathing, and amniotic fluidvolume are the most significant variables.


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The non-stress test and fetal breathingmovements are suppressed when the pH fallsbelow 7.2.

If the fetal pH falls below 7.10 fetal tone andfetal movements become abolished

The presence of oligohydramnios with all ofthe other variables of the biophysical profilebeing normal may reflect chronicuteroplacental insufficiency


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Components of the Biophysical Profile Score

Component Definition

Non-stress testTwo or more fetal heart rate accelerations peak (but do notnecessarily remain) at least 15 beats per minute above thebaseline and last 15 seconds from baseline to baseline withina 20-minute period with or without fetal movement discernibleby the woman.

Amniotic fluidvolume A single 2 cm x 2 cm pocket is considered adequate or AFIgreater than 5.0 cm .

Fetal breathingmovements

One or more episodes of rhythmic fetal breathing movementsof 30 seconds or more within 30 minutes.Hiccups are considered breathing activity.

Fetal movements At least three discrete body or limb movements.Episodes of continuous movement are considered as a singlemovement.

Fetal tone One or more episodes of extension of a fetal extremity ortrunkwith return to flexion, or opening or closing of a hand


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Perinatal Mortality and the Biophysical Profile Score

Score Interpretation Perinatal Mortality/10008- 10 Normal 1.86*

6 Equivocal

9.76

4 Abnormal 26.32 Abnormal 94.00 Abnormal 285.7

*The perinatal mortality is 0.8/1000 for structurally normal fetuses with a normal testwithin 7 days.


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Maternal and Fetal Causes of Stillbirth within One Weekof a Normal Biophysical Profile Score

Maternal FetalPlacental abruption

Diabetic ketoacidosis

Sickle cell crisisDrug overdoseMotor vehicle accidentAcute myocardial infarction

Acute alcohol poisoning

Fetomaternal hemorrhageCord prolapse

Ruptured membranesVase previaCord entanglementUmbilical artery

thrombosis


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Interpretation of an Equivocal or Abnormal BPP

The absence of a biophysical variable may reflect:

Normal fetal activity and sleep cyclesAn inability of the central nervous system to perform that

functionHypoxiaExternal influences

Fetal breathing movements may beStimulated by caffeine and hyperglycemia.Inhibited by hypoglycemia, maternal supinehypotension, cigarette smoking, alcohol, diazepam andmeperidine.


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Action for Equivocal or Abnormal BPP

The term fetus is generally delivered for a score of 6. However, a score of 6 in a preterm fetus is usuallyrepeated in 12 to 24 hours. In the interim, antenatalsteroids may be given for pregnancies of less than 34weeks of gestation.

Delivery is usually indicated for BPP score of 4 or less.

Oligohydramnios always requires further evaluation.

Patients with a biophysical profile score of 6 or less should beconsidered for transfer to Labor and Delivery for further

observation or delivery and physician notified.


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Special Considerations

Rupture of the membranes does not alter the short-termsonographic variables of the biophysical profile in thehealthy fetus.

The negative predictive value of a normal biophysicalprofile score is not as high with an anomalous fetus, incontrast to a structurally normal fetus.

Sudden fetal deaths have been reported following a

normal biophysical profile score in fetuses withgastroschisis, omphalocele, and diaphragmatic hernia.


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Special Considerations

The observation of an abnormal biophysical profile in ananomalous fetus does not correlate very well with thepresence of hypoxia.

The biophysical profile score cannot be used in fetuses

with congenital muscular diseases or central nervoussystem conditions that would affect muscular function.

If an anomalous fetus had a previously normal

biophysical profile score, a decreasing score should beconsidered an indication of compromise

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