ASSESSMENT OF FETAL WELL-BEING Selçuk Özden MD, Prof

INTRODUCTION The goal of antepartum fetal assessment is to both identify fetuses at risk of intrauterine death or other complications of intrauterine asphyxia and intervene to prevent these adverse outcomes, if possible. 

PHYSIOLOGICAL BASIS FOR FETAL TESTING  Antepartum testing is based on the premise that the fetus responds to hypoxemia with a detectable sequence of biophysical changes, beginning with signs of physiological adaptation and potentially ending with signs of physiological decompensation.

SEQUENCE OF FETAL RESPONSE TO STRESS

PHYSIOLOGICAL BASIS FOR FETAL TESTING Fetal biophysical activities (eg, heart rate, movement) are sensitive to fetal oxygenation and pH levels, Changes in fetal biophysical activities occur in response to hypoxemia and acidemia.

PHYSIOLOGICAL BASIS FOR FETAL TESTING Fetal biophysical parameters can also be affected by factors unrelated to hypoxemia, such as: Gestational age, Maternal medication/smoking,  Fetal sleep-wake cycles, Fetal disease/anomalies.

INDICATIONS FOR FETAL SURVEILLANCE American College of Obstetricians and Gynecologists (ACOG) practice bulletin on antepartum fetal surveillance suggests antepartum testing for "pregnancies in which the risk of antepartum fetal demise is increased" It is not possible to list every clinical setting where tests for antepartum fetal assessment 

INDICATIONS FOR FETAL SURVEILLANCE Diabetes  Hypertensive disorders  Fetal growth restriction Twin pregnancy  Postterm pregnancy Decreased fetal activity Systemic lupus erythematosus Antiphospholipid syndrome  Sickle cell disease Isoimmunization Oligohydramnios or polyhydramnios  Prior fetal demise Preterm premature rupture of membranes  Other (Nonimmune hydrops, maternal cyanotic heart disease, poorly controlled maternal hyperthyroidism, and maternal vascular diseases) POSSİBLE İNDİCATİONS FOR ANTENATAL TESTİNG Advanced maternal age Obesity Abnormalities in first and second trimester Down syndrome maternal analyte screening results  Major fetal structural anomalies

MAIN TECHNIQUES FOR FETAL ASSESSMENT The nonstress test (NST), Biophysical profile, Modified biophysical profile, Contraction stress test (CST), Fetal movement count. Assessment of amniotic fluid volume and Doppler velocimetry provide additional information about fetal status. 

FETAL MOVEMENT COUNTING Objective maternal assessment of fetal movements is based on evidence that fetal movement decreases in response to hypoxemia.  Women with decreased fetal movement should undergo further fetal assessment, Available evidence does not support a clear fetal movement threshold or "alarm limit" indicating when the risk of fetal death or injury is increased.

FETAL MOVEMENT COUNTING In the second and third trimesters, sonography reveals a wide range of movements of Fetal trunk (eg, bending, startle, hiccup, breathing, rotation), Limbs (eg, stretch, hand to face, opening and closing of hands), and The face and head (eg, head rotation, suck, yawn, tongue protrusion).

FETAL MOVEMENT COUNTING Normal quantity and quality of fetal movement and other types of fetal biophysical activity (breathing movements, tone) virtually ensures functional integrity of fetal regulatory systems. 

FETAL MOVEMENT COUNTING Mothers perceive 33 to 88 percent of sonographically visualized fetal movements. Fetal movement increases throughout day, with peak activity late at night. The frequency of fetal movement in normal pregnancy is probably constant throughout the third trimester. At least 40 percent of pregnant women become concerned about decreased fetal movement one or more times during pregnancy

FETAL MOVEMENT COUNTING When these regulatory systems are subjected to mild hypoxemia, decreased fetal movement (DFM) is believed to represent a compensatory fetal behavioral response. As hypoxemia becomes more severe and prolonged, compensatory responses may fail to protect the fetus, eventually leading to fetal injury or death.

FETAL MOVEMENT COUNTING Diagnosis of DFM: There is no consensus on diagnosis of DFM. The best diagnostic criteria are controversial because the level of fetal movement that reliably distinguishes a healthy fetus from a fetus at increased risk of adverse outcome has not been determined

FETAL MOVEMENT COUNTING Kick Counts: Various methods for defining an alarm limit have been proposed: Perception of least 10 fetal movements (FMs) over up to two hours when the mother is at rest and focused on counting ("count to 10" method) Perception of at least 10 FMs during 12 hours of normal maternal activity Perception of at least 4 FMs in one hour when the mother is at rest and focused on counting Perception of at least 10 FMs within 25 minutes in pregnancies 22 to 36 weeks and 35 minutes in pregnancies 37 or more weeks of gestation

AMNIOTIC FLUID VOLUME In the hypoxemic fetus, cardiac output is redirected to the brain, heart, and adrenals and away from less vital organs, such as the kidney; The reduction in renal perfusion leads to decreased fetal urine production, which may result in decreased amniotic fluid volume (oligohydramnios) over time.

AMNIOTIC FLUID VOLUME Mean amniotic fluid volume during normal pregnancy

AMNIOTIC FLUID VOLUME Sonographic determination of the single deepest amniotic fluid pocket (SDP) Four quadran Amniotic Fluid İndex (AFI). The SDP and the amniotic fluid index (AFI) method are equivalent in their prediction of adverse outcome in singleton pregnancies

AMNIOTIC FLUID VOLUME Interpretation of Single deepest pocket technique Oligohydramnios – depth <2 cm Normal – depth ≥2 cm and <8 cm Polyhydramnios – depth ≥8 cm

AMNIOTIC FLUID VOLUME Interpretation of Amniotic Fluid İndex. AFI measurement is calculated by first dividing the uterus into four quadrants using the linea nigra for the right and left divisions and the Oligohydramnios – AFI ≤5 cm Normal – AFI >5 cm and <24 cm Polyhydramnios – AFI ≥24 cm

NONSTRESS TEST (NST) The NST is the most common cardiotocographic method of antepartum fetal assessment. It is noninvasive and can be performed in any setting with an electronic fetal monitor. There is no direct risk of maternal or fetal injury associated with nonstress testing.

NONSTRESS TEST Heart rate accelerations, spontaneous or provoked (eg, by vibroacoustic stimulation), have been shown to be a good indicator of normal fetal autonomic function and absence of acidosis and neurologic depression.

INTERPRETATION of NONSTRESS TEST Reactive NST :  The NST test is reactive from 33 weeks to term if there are two or more fetal heart rate accelerations reaching a peak of at least 15 beats per minute (bpm) above the baseline rate and lasting at least 15 seconds from onset to return to baseline in a 20 minute period

INTERPRETATION of NONSTRESS TEST Reactive NST 

INTERPRETATION of NONSTRESS TEST Nonreactive NST — An NST is nonreactive if it does not meet acceleration criteria for a reactive NST. The fetal heart rate should be monitored for at least 40 minutes but no more than 120 minutes before interpreting the test as nonreactive.

INTERPRETATION of NONSTRESS TEST Nonreactivity may be a sign of fetal hypoxemia or acidosis. The mean umbilical vein pH associated with a nonreactive NST is 7.28 ± 0.11 Other causes of nonreactivity include fetal immaturity, quiet fetal sleep, maternal smoking (women who smoke should not smoke proximate to an NST), fetal neurologic or cardiac anomalies, sepsis, or maternal ingestion of drugs with cardiac effects

INTERPRETATION of NONSTRESS TEST The main advantage of the NST over the contraction stress test (CST) is that it does not require an intravenous line, oxytocin, or contractions. Disadvantages are that the false-negative (0.2-0.65%) and false- positive rates (55-90%) are higher than for the CST.

VIBROACUSTIC STIMULATION TEST A nonreactive test finding resulting from fetal quiet sleep is a major source of falsely alarming tests Vibroacoustic stimulation (VAS) (i.e., stimulating the fetus with a noxious vibration and noise) is effective in producing a state change, fetal startle movements, and increased FHR variability.

CONTRACTION STRESS TEST (CST) The contraction stress test (CST) (oxytocin challenge test) is based on the fetal response to a transient reduction in fetal oxygen delivery during uterine contractions. If the fetus becomes hypoxemic (fetal arterial pO2 below 20 mm Hg) fetal chemoreceptors and baroreceptors, as well as sympathetic and parasympathetic influences, respond by reflex slowing of the fetal heart rate (FHR), which may manifest clinically as late decelerations

CONTRACTION STRESS TEST Myometrial contraction ↓ Intervillous blood flow↓ O2 Exchange ↓ İf there is uteroplacental pathology Late Deceleration Early Late

CONTRACTION STRESS TEST Contraction stress test is applied by : 1- Oxytocine challenge test (OCT) : OCT uses intravenous oxytocin to cause repetitive uterine activity.

CONTRACTION STRESS TEST Nipple stimulation test to induce uterine contractions is usually successful for contraction stress testing . Method : rubbing one nipple through her clothing for 2 minutes or until a contraction begins. This stimulation ideally will induce a pattern of three contractions per 10 minutes. If not, after a 5-minute interval, she is instructed to retry nipple stimulation to achieve the desired pattern.

CONTRACTION STRESS TEST Fetal heart rate and uterine contraction are recorded simultaneously. After a contraction pattern is established with at least three contractions in 10 minutes, evaluation is possible.

CONTRACTION STRESS TEST Late decelerations are characterized by a gradual decrease and return to baseline of the fetal heart rate associated with uterine contractions. 

CONTRACTION STRESS TEST

CONTRACTION STRESS TEST Major drawbacks related to use of the CST include The need to stimulate contractions with intravenous oxytocin, The contraindication to inducing contractions in some conditions (eg, placenta previa), The high false-positive rate. (35- 65%) The CST is seldom performed given the wide availability of other tests (eg, nonstress test, biophysical profile)

CONTRACTION STRESS TEST In contrast, the false-negative rate (ie, rate of antepartum stillbirth within one week of a negative test) is very low (0.04%), Thus providing reassurance of adequate fetal oxygenation after a normal test result. Continuous FHR monitoring and at least 3 contractions of ≥40s duration within 10 minutes are necessary.

CONTRACTION STRESS TEST Negative: No late or significant variable decelerations Positive: Late decelerations following ≥50 percent of contractions, even if there are <3 contractions in 10 minutes Equivocal - suspicious: Intermittent late decelerations or significant variable decelerations Equivocal - hyperstimulatory: Decelerations with contractions occurring more frequently than every 2 minutes or lasting >90s Unsatisfactory: <3 contractions in 10 minutes or uninterpretable FHR tracing

BIOPHYSICAL PROFILE The biophysical profile (BPP) combines the NST with the following parameters: Amniotic fluid volume (AFV), Fetal breathing movements, Fetal body movements, and  Reflex/tone/ flexion extension movements 

BIOPHYSICAL PROFILE

BIOPHYSICAL PROFILE Components and Scores of Biophysical Profile

BIOPHYSICAL PROFILE Interpretation of Biophysical Profile Score

MODIFIED BIOPHYSICAL PROFILE Biophysical profile is time consuming So other combinations of components may be used. Vibroacustic NST + AFI two times in a week NST + AFI <5 cm

DOPPLER VELOCIMETRY Doppler velocimetry is a noninvasive method of assessment Measurement of blood flow velocities in the maternal and fetal vessels provides information about uteroplacental blood flow and fetal responses to physiologic challenges.

DOPPLER VELOCIMETRY Umbilical artery — Umbilical artery Doppler assessments are most useful for monitoring fetuses with early-onset growth restriction due to uteroplacental insufficiency. Progressive reduction of umbilical artery diastolic flow is associated with worsening destruction of placental villus vasculature When monitoring the growth-restricted fetus, umbilical artery Doppler should be used with standard fetal surveillance (nonstress test and/or biophysical profile score).

DOPPLER VELOCIMETRY Umbilical artery Resistance to blood flow is evaluated by indexes Ratio of systolic blood flow to diastolic is evaluated semiquantitively.

DOPPLER VELOCIMETRY Pathological findings: S/D ratio > 95 p Absent end diastolic flow) Reverse flow

DOPPLER VELOCIMETRY Middle cerebral artery — Doppler assessment of the fetal middle cerebral artery-peak systolic velocity is the best tool for monitoring for fetal anemia in at-risk pregnancies Middle cerebral artery Doppler is under investigation as an additional tool for surveillance of pregnancies complicated by growth restriction

DOPPLER VELOCIMETRY

DOPPLER VELOCIMETRY Uterine artery — A number of investigators have explored the use of uterine artery Doppler for third trimester fetal assessment among women with complicated pregnancies, but its role in these settings has not been clearly defined

DOPPLER VELOCIMETRY Ductus venosus: Retrograde a-wave (1, atrial contraction, called an a-wave; 2, ventricular systole; 3, ascent of annulus; 4, diastole)

CHOICE of TEST Although observational studies have described the use of the nonstress test (NST), contraction stress test (CST), and biophysical profile score (BPP) for monitoring high-risk pregnancies, no method has been evaluated in well-designed randomized trials and it is not clear which method, if any, is superior.

MANAGEMENT OF ABNORMAL TEST RESULTS Given the high rate of false-positive tests, an abnormal test result is generally followed by additional testing with a different test (eg, contraction stress test [CST] or biophysical profile [BPP] after a nonreactive nonstress test [NST]) to provide more information about fetal status.

TIMING Testing should begin as soon as an increased risk of fetal demise is identified and delivery for perinatal benefit would be considered if test results are abnormal. 

REFERENCES Cuningham G, Williams Obstetrics, 24 th edition, 2014, McGraw-Hill Education Kevin P. Hanretty. Obstetrics Illustrated, Sixtth ed. Churchill Livingstone, London, 2004 Alan H. DeCherney,, CURRENT Diagnosis & Treatment Obstetrics & Gynecology, 11th edition, The McGraw-Hill Companies, 2013 Creasy And Resnik’s Maternal-fetal Medicine, Seventh Edition, Elsevier Saunders, 2014