Ant-partum Fetal Evaluation

Professor Hassan Nasrat

By the end of this Lecture you should be able to :-List the objectives of antepartum fetal surveillance -Discusses the fetal response to hypoxia (patho-physiology of fetal response to hypoxia): The compensation and decomposition of the fetus to hypoxia.

-List the methods of fetal monitoring:

OFetal Movements count:oElectronic Fetal Heart Monitoring (Non-Stress Test

and Contractions Stress test):oBiophysical Profile (BPP):oViboracustic Stimulation:oDoppler Blood Flow:

-For Each method you should be able to describe : The principle, technique and interpretation.

Objectives and indications of prenatal fetal monitoring

Objectives and indications of prenatal fetal monitoring

Primary goal: To Prevent fetal Death

Secondary goal: Prevent neurologic injury from prolonged exposure to intrauterine hypoxia.

Indications For Fetal Surveillance Indications For Fetal Surveillance

1.Patients at high risk of uteroplacental insufficiency e.g.: Prolonged pregnancy.HypertensionDiabetes Previous stillbirthSuspected FGRMultiple pregnancyAdvanced maternal ageAntiphospholipid syndrome

2.When other tests suggest fetal compromise e.g.: Suspected FGR (on clinical examination) Decreased fetal movementsOligohydramnios

Indications For Fetal Surveillance Indications For Fetal Surveillance

Neurological Maturation of Fetal function and

Patho-physiology of fetal Hypoxia:

Neurological Maturation of Fetal function and

Patho-physiology of fetal Hypoxia:

Neurological Maturation of Fetal function

Neurological Maturation of Fetal function

The Fetal Tone And Movements: (Between 7 -9 Weeks)

Fetal Heart Reactivity: The Parasympathetic then the sympathetic system.

The Breathing Movements: Are Controlled By The Breathing Center In Brain Stem. Breathing Movements Start To Appear From Early Second Trimester.

Maturation of the fetal neurological function occurs in stages:

Pathophysiology of fetalHypoxia

Pathophysiology of fetalHypoxia

General principles in Interpretation of Fetal monitoring

General principles in Interpretation of Fetal monitoring

Interpretation of any of the methods of fetal monitoring should take in consideration some factors:

gestational age, maternal conditions (E.g. administration of steroid for fetal lung maturity is associated with reduced BPP for period up to 3 days), Fetal condition (e.g. GR, anemia, arrhythmia).

more than one method should be used because of the limited sensitivity of most of them.

Interpretation of Fetal monitoring Interpretation of Fetal monitoring

Depending on:The Results Of The Tests.Gestational Age.And Overall Clinical Situation,

delivery may be warranted if the risks of continuing the pregnancy outweigh the benefits .

Fetal Movements count:

Electronic Fetal Heart Monitoring (Non-Stress Test and contractions stress test):

Biophysical Profile (BPP):

Viboracustic Stimulation:

Doppler Blood Flow:

Methods of fetal surveillance during pregnancy Methods of fetal surveillance during pregnancy

1) Maternal Assessment of Fetal Activity (Fetal Movement Count Chart):1) Maternal Assessment of Fetal Activity (Fetal Movement Count Chart):

Principle:Normal fetal movement is a sign of functional integrity of fetal neuro-regulatory systems. In the presence of mild hypoxemia, the fetus compensate by decreased frequency and strength of movements. Hence decreased fetal movement is considered a warning sign for further fetal evaluation. The Technique: A special chart called “kick Chart” is used by the mother to record her baby’s movement over a period of time. If the fetus moves less than certain number of movements the mother is asked to report to the clinic.

Advantage: low cost but also can be offered to almost all women

The following three criteria are the most commonly used :

Perception of at least 10 FMs during 12 hours of normal maternal activity

Perception of at least 10 FMs over two hours when the mother is at rest and focused on counting “Cardiff Count-to-Ten chart”

Perception of at least 4 FMs in one hour when the mother is at rest and focused on counting.

DD of decreased movements “DFM”:

Transient decrease in fetal activity can be due to fetal sleep states.

Maternal drug use (e.g. sedatives), or maternal smoking.

Inadequate perception of movements by the mother. E.g. early gestational age, decreased/increased amniotic fluid volume, maternal position (sitting or standing versus lying), fetal position (anterior position of the fetal spine), obesity, anterior placenta, and maternal physical activity (or just being mentally distracted).

2) Electronic Fetal Heart Rate Monitoring 2) Electronic Fetal Heart Rate Monitoring

Principle: Monitoring of fetal heart activities is indirect way for assessment of fetal oxygen status. Fetal hypoxia affects the cardiac control centers, and result in diminished heart activities “rate, variability and reactivates” through the autonomic nervous system.

A Doppler ultrasound transducer for the FH activities and a tocotransducer to detect uterine contractions. Fetal movements are usually recorded by the patient

The technique: Electronic fetal heart monitoring depends on recording fetal heart activities in response to uterine contractions and or fetal movments

Types antenatal fetal heart rate monitoring:

(1) The Non Stress Test “NST” and

(2)The Contraction Stress Test “CST” or sometimes called oxytocin stress test.

The NST is the most commonly used method of antepartum fetal assessment. It is noninvasive (unlike the CST) It has no direct maternal or fetal risks, and virtually no contraindication.

Interpretation: the results of a NST is interpreted as either reassuring or non reassuring based on criteria:The rate of the fetal heart. The variability “beat to beat variation” Response to uterine contractions and/or fetal movements:

Non-stress test “NST”: Non-stress test “NST”:

Reassuring patterns “Reactive test”: the following criteria should be fulfilled over 20 minutes of fetal monitoring:1.A basal FHR within normal (110-160 bpm),2.Variability range (5-25 beats), 3.At least two accelerations of the FHR of approximately 15 bpm amplitude and for 15 seconds' duration. If these criterions are not met the test may be extended for further 20 minutes. Non –reassuring pattern “Non-reactive test”: The test is labeled as non reactive if after 40 minutes the criteria for reactivity are not met.

Reassuring patterns “Reactive test”

In some cases if the test is non-reactive, acoustic stimulation may be used to apply a sound stimulus for 1 to 2 seconds (see vibroacoustic stimulation).

Interpretation of the (NST) or Cardiotocogram “ CTG “results: should take in consideration the gestational age (the response of the fetal heart depends on maturation of the fetal autonomic nervous system). Therefore it is difficult to interpret the test before 24-26 weeks.

The presence of a reassuring pattern indicates that there is no fetal hypoxemia only at the time of testing. The frequency of doing the test is based on clinical judgment and the indication for testing. It may be performed at daily to weekly intervals as long as the indication for testing persists.

Differential diagnosis of Non Reactive Test: Causes other than fetal hypoxia should be considered such as: Benign and temporary non-reassuring test due to fetal immaturity, maternal smoking, or fetal sleep. , or maternal smoking.

Fetal neurological or cardiac anomalies and sepsis.

Maternal ingestion of drugs with cardiac effects.

Principle: uterine contractions cause reduction in blood flow to the intervillous space and transient state of hypoxia.

A fetus with inadequate placental reserve (i.e. uteroplacental insufficiency) would demonstrate late decelerations in response to the transient hypoxia of uterine

The Contraction Stress Test “CST” The Contraction Stress Test “CST”

The Technique:

1The CST is ideally conducted in the labor and delivery suite or in an adjacent area.

2uterine contractions is induced using oxytocin infusion or nipple stimulation technique. The aim is to induce at least three contractions within 10 minutes.

The Contraction Stress Test “CST” The Contraction Stress Test “CST”

Contraindications patients at high risk for premature labor,placenta previa previous classic cesarean section or uterine surgery.

Interpretation of the Contraction Stress Test:Negative: if no deceleration occurred during the period of the test. Positive: if late deceleration occur.

The Contraction Stress Test “CST” The Contraction Stress Test “CST”

Principle: It depends on stimulation of the fetus by an artificial burst of noise produced by a hand-held battery-powered artificial larynx. It generates sound pressure levels measured at 1 m in air of 82 dB with a frequency of 80 Hz and a harmonic of 20 to 9,000 Hz.

The goal is to alter the fetal behavioral state, wake a sleeping fetus, and provoke accelerations in the heart rate thus shorten the length of the NST.

Vibroacoustic stimulation (VAS) Vibroacoustic stimulation (VAS)

Fetal BPP is based on the use of real-time ultrasonography to perform an in utero physical examination and evaluate dynamic functions reflecting the integrity of the fetal CNS (i.e. oxygenation) Principle: the physical activities that reflect the biological integrity of the fetal central nervous system include five parameters. Four are based on ultrasound studies include: Fetal breathing movements (FBM), fetal body movement, fetal tone, and amniotic fluid volume and

The fifth is the result of NST.

Fetal Biophysical Profile “BPP” Fetal Biophysical Profile “BPP”

Fetal Biophysical Profile “BPP” Fetal Biophysical Profile “BPP”

It is important to realize the following:

The presence of all the parameters is sign of healthy and well-oxygenated

system.

As the number of absent parameter increases, the likelihood of fetal

compromise (hypoxia) increases.

The fetal biophysical activities that appear earliest in fetal development are the

last to disappear

The Fetal Tone And Movements: (Between 7 -9 Weeks)

Fetal Heart Reactivity: The Parasympathetic then the sympathetic system.

The Breathing Movements: Are Controlled By The Breathing Center In Brain Stem. Breathing Movements Start To Appear From Early Second Trimester.

Appear Dis-Appear

Fetal Biophysical Profile “BPP” Fetal Biophysical Profile “BPP”

Diminished Amniotic fluid volume “oligohydramnios” reflects

long-term fetal (Chronic) hypoxia since it results from

diminished fetal urine output. This takes place secondary to

compensatory redistribution of fetal circulation.The Other parameters reflect hypoxia and stress at the time of the test

Fetal Biophysical Profile “BPP”:

Interpretation of the BPP “The Fetal BPP Score” Each of the five parameters of the BPP is awarded 2 points. The highest score a fetus can receive is 10, if all parameters are satisfactory.

The lower the score the higher the risk of fetal compromise, fetal hypoxia and acidosis

Relation between BPP Score and the Fetal Cord PH at BirthRelation between BPP Score and the Fetal Cord PH at Birth

A score of 8 or more is interpreted as normal with a very little risk of fetal death within 1 week (estimated as <1 in a 1,000).

A score of 6 out of 10 may A repeat test should be undertaken or delivery if the fetus is at term.

A score of 4 out of 10 should raise serious concern of fetal compromise, with a high risk of fetal death, such that delivery would be indicated in most situations.

A score of 0 to 2 out of 10 is an emergency and delivery should occur depending on the clinical circumstance.

Fetal Biophysical Profile “BPP”

Principle of The Modified BPP: Because FHR accelerations are one of the last of biophysical variables to develop, therefore if the NST is reactive, then the other variables should be present.

Also adequate amniotic fluid usually indicates that the fetus is not suffering from chronic placental insufficiency.

The modified BPP is considered normal if the fluid volume is adequate (AFI greater than 5 cm) with a reactive NST.

The modified BPP has the advantages that it takes less time

Doppler Ultrasound Doppler Ultrasound

Principle: Doppler ultrasound is a noninvasive assessment of the blood flow in the fetal, maternal, and placental circulations. Various blood vessels have been investigated using Doppler velocimetry, including the maternal uterine artery, fetal middle cerebral artery, and fetal ductus venosus

Doppler Ultrasound Doppler Ultrasound

In normal pregnancy the placental vascular

resistance decreases as the pregnancy

progresses, hence the umbilical blood flow

increases.

Doppler Ultrasound Doppler Ultrasound

In cases with placental insufficiency e.g. pre-eclampsia, or FGR (fetal growth restriction) the Doppler blood flow study shows decreased blood flow especially during diastole. The fetus would also try to compensate by compensate by shunting most of the blood flow to the brain, heart, and adrenal glands at the expense of the placenta and peripheral circulation, a phenomena known as “ brain-sparing reflex”.

Therefore the Doppler blood flow study of cerebral vessels would show increase in blood flow in the fetal cerebral circulation.

Doppler Ultrasound

The technique: Doppler hemodynamic blood flow study is based on directing beam of ultrasound waves with a particular frequency on to the desired blood vessel.

The beam returns with different frequency proportional to the speed and direction of flow of the blood cells in the studied vessel. The difference between the frequency of the emitted beam and the frequency of the returned beam is known as the “Doppler shift” that reflects the blood flow velocity, and can be recorded and displayed electronically.

Doppler Ultrasound

Interpretation of Doppler Ultrasound:

an increased difference between the peak blood flow during systole and during diastole reflect increased placenta resistance.

In severe cases there may be no flow during diastole or ever a reversal of blood flow during the diastolic phase of the cardiac cycle.

Absent end diastolic blood flow Absent end diastolic blood flow

Normal blood flow notice S/D ratio is a positive Normal blood flow notice S/D ratio is a positive

Reversed end diastolic blood flow Reversed end diastolic blood flow