11-evaluation Of Fetal Well-being Nov2000

Dr. Majed Alshammari, Nov.. 2001

Antenatal & Intrapartum Fetal Monitoring OBJECTIVES OF EVALUATION: Depending on gestational age, antepartum & intrapartum stage: Location Viability Number Biometry (size, growth) Placental exam Amniotic fluid volume assessment Morphology Biophysical profile Adaptation to stress Lung Maturity Prediction of hypoxic-acidotic insults TOOLS OF EVALUATION a. History. b. Physical Exam. c. Laboratory Investigations. d. Ultrasound. e. Prenatal Screening Tests. f. Invasive Procedures g. Doppler Flow Studies. h. Tests of Fetal Lung Maturity i. Biophysical Profile (BPP) j. Electronic Fetal Heart Rate Monitoring. k. Methods of Intrapartum Fetal Monitoring A.

History Amenorrhea Pain & bleeding in first trimester Pregnancy symptoms Significant past obstetrical and general history Fetal movement first at 16-20 weeks.  Pain, bleeding, leaking in 2nd and 3rd trimester. B.

Physical Exam General: BP, Temp, edema, anemia Size of uterus Signs of abortion  Abdominal obstetrical examination Uterine fundal growth 12 weeks: just above pubis 20-24 weeks at umbilicus (variable) 24-34 weeks: SFH (cm) = gestational age (wks) FHR auscultation starting at 11-12 weeks by daptone 1

FHR in early gestation may reach 160-170 bpm, subsequently become less (120-160) due to autonomic maturation. Do not confuse other sounds e.g. fetal movement, maternal uterine pulse C.

D.

Laboratory Investigations Pregnancy test Urine β HCG Serum β HCG: level normally doubles every 48 hrs. Routine Investigations CBC Blood group and Rh type Rh antibodies VDRL, Rubella, Hepatitis FBS Urine r/m and c/s Other tests according to case e.g. APL in recurrent abortions, RFT in renal disease …etc. Ultrasound I. In the First Trimester Objectives Finding and location of gestational sac: see table below. Viability of fetus: see table below. Number of fetuses Nuchal translucency: chromosomal abnormalities. Vaginal Ultrasound 5(TVS) weeks

Interauterine Sac Cardiac Pulsation

•

β HCG IU/L

>

1200

Abdominal Ultrasound (TAS) 6 weeks β HCG > 5000 IU/L

6 weeks

7 weeks

Failure to document fetal pulsation at 6 weeks by TVS or 7 weeks by TAS indicates abortion, if date is accurate. These findings depend on good resolution ultrasound imaging.

II. Ultrasound in second and third trimesters A single midtrimester 16-20 weeks (~18 weeks) is recommended for all women. Objectives: 1. 2. 3. 4. 5. 6. 7. 8. 9.

Number of fetuses Presentation Viability Amniotic fluid volume Placental localization Fetal biometry: BPD, HC, AC, FL Basic morphological surveillance Detailed morphological exam, if required Fetal echocardiography if high risk congenital heart 2

E.

Prenatal Screening Tests (Triple Screening) • 3 biochemical tests: a-fetoprotein, bHCG, S. estriol • Done around 15-18 weeks • • • • •

The test picks up about 80% of neural tube defects and 70% Down syndrome. Normograms results gives risk of chromosomal abnormalties, mainly trisomy 21, but not diagnsotic. Very high false positive requiring invasive procedures for comfirmatoin. Diagnosis confirmed by ultrasound and/or amniocentesis. Done where abortion laws are permissive. Not practiced in Kuwait.

F. Invasive Procedures Chorionic villous sampling 1. Amniocentesis 2. Cordocentesis Not practiced in Kuwait on routine basis for religious issues.  For prenatal diagnosis of genetic diseases, and management of other diseases e.g. Rh Isoimmunization, hydrops, suspected infection. Complications of procedures: i. Fetal loss: CVS 1%, Amnio 0.5%, Cordo 2-3% ii. Bleeding iii. Infection iv. Membrane rupture G. Doppler Flow Study In cases of utero-placental insufficiency, fetal blood flow redistribution occur more to (less resistance) fetal brain, heart and adrenals and less to (less resistance) abdominal viscera and lower limbs. Measurements of fetal umbilical artery blood flow (represents lower body flow) and cerebral artery flow may show this asymmetrical changes. Systolic: diastolic ratio indicates the resistance index • Decreased diastolic flow, becoming absent or even reversed correlates with the severity of impaired blood flow (increase resistance) disease. H. Tests of Fetal Lung Maturity I. Lecithin-to-Sphingomyelin (LS) Ratio L & S are phospholipids components of surfactants. Lung maturity is related to surfactant maturity. Before 34 weeks, L & S are present in amniotic fluid in similar concentrations. After 34 weeks, L begins to rise relative to S. Increased Respiratory distress if LS ratio is < 2 Sample is obtained by amniocentesis.

II. Phosphatidylglycerol (PG) PG enhances surfactant function Identification of PG in amniotic fluid (positive test) is associated with lung maturity Not contaminated by blood, meconium, or vaginal secretions so can be sampled directly from amniotic fluid in

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the vagina.

I.

Biophysical Profile (BPP) Fetal movement ≥ 3 times Breathing movement ≥ 30 seconds Tone: ≥ 1 limb flexionextension Amniotic fluid ≥ 2 cm perpendicular Reactive NST Max. Total Score Ultrasound exam over 40 minutes maximum

Present 2 2

Absent 0 0

2

0

2

0

2 10

0

Total score of 8 or 10 is normal Total score of 6 is equivocal and should be repeated in 12-24 hours Total score of 4 or less is abnormal, consider delivery soon if viable fetus. J.

Electronic Fetal Heart Rate (FHR) Monitoring.

I.

Contraction stress test (CST): Study of FHR response to induced stress by either giving oxytocin drugs or nipple stimulation. Inadequate fetal oxygenation with the uterus at rest will be transiently worsened by uterine contractions resulting in fetal hypoxemia and late deceleration • Most used in USA but not very popular elsewhere because of its risk.

II. Non-Stress Test (NST) • Study of FHR response to fetal movement.

• • • •

Fetal activity cycle, fetus may go into inactive “sleep” period for maximum 2 hours. FHR is dependent on maturation of autonomic system Without labor (Antenatal), is highly sensitive and specific test Reactive Pattern:

Baseline FHR 120-160 bpm ≥ 2 accelerations in 20 minutes Acceleration amplitude > 15 beats from baseline, lasting > 15 seconds Variability 15 beats (5-10 if premature fetus) No periodic or significant decelerations > 30 beats.

n-Reactive Pattern 4

Lack of reactive criteria over 40 minutes. Always of concern ante-partum & delivery is generally indicated.

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K.

INTRAPARTUM FETAL MONITORING

Introduction: Fetal Physiology Transient and repetitive episodes of hypoxemia, even at the level of the central nervous system (CNS), are extremely common during normal labor. Generally well tolerated by the fetus. Levels that are ominous to an infant or adult are commonly seen in normal newborns. Only when hypoxia and resultant metabolic acidemia reach extreme levels is the fetus at risk for long-term neurologic impairment. Fetal oxygen extraction from the maternal circulation is well adapted even with the additional stress of normal labor and delivery. However, alterations in the fetoplacental unit resulting from labor or intrapartum complications may compromise fetal oxygenation. Oxygen delivery is critically dependent on uterine blood flow. Factors that decrease placental blood flow Uterine contractions Maternal position Conduction anesthesia Pathologic situations: Preeclampsia, abruptio placentae, chorioamnionitis, and others. Cord compression by entanglement, oligohydramnios, knots, or prolapse. Susceptible fetuses Methods of Intrapartum Fetal Monitoring: I. Cardiotocography: Most commonly applied Electronic monitoring of FHR and uterine contractions shows the following patterns, each pattern can be explained by different mechanism of fetal hypoxemia: Normal Pattern Reduced Variability Baseline Tachycardia/Bradycardia Early Decelerations Late Decelerations Variable Decelerations Other Patterns e.g Sinusoidal Normal Pattern: FHR Accelerations Are common periodic changes in labor and are nearly always associated with fetal movement. Virtually always reassuring and almost always confirm that the fetus is not acidotic at that time FHR Variability A useful indicator of fetal CNS integrity. May serve as a barometer of the fetal response to hypoxia. Factors such as a fetal sleep cycle or medications may decrease the activity of the CNS and the variability of the FHR. Early Decelerations Benign changes caused by fetal head compression. Seen in the active phase of labor. 6

They are usually shallow and symmetrical. Reach their nadir at the same time as the peak of the contraction. Baseline Tachycardia: Causes Severe and prolonged fetal hypoxia maternal fever Fetal anemia Intraamniotic infection i.e. chorioamnionitis Congenital heart disease Hyperthyroidism Prolonged Deceleration An isolated, abrupt decrease in the FHR to levels below the baseline that lasts at least 60-90 seconds. Always of concern and may be caused by virtually any mechanism that can lead to fetal hypoxia. Variable Decelerations Umbilical cord compression or, occasionally, head compression. Abrupt onset and return Vary in depth, duration, and shape. Frequently preceded and followed by small accelerations of the FHR. Coincide in timing and duration with the compression which coincides with the timing of the uterine contractions. Generally associated with a favorable outcome. Non-reassuring if: Persistent. Progressively deeper to less than 70 bpm lasting greater than 60 seconds. Persistently slow return to baseline . Late Decelerations U-shaped, gradual onset and return, usually shallow 10-30 beats per minute. Reach their deepest point after the peak of the contraction. A result of CNS hypoxia; in more severe cases, it may be the result of direct myocardial depression. Sinusoidal Heart Rate Pattern Regular oscillation of the baseline long-term variability resembling a sine wave, lasting at least 10 minutes, Rare and associated with fetal anemia, sedatives and acidosis.

•

CTG prediction of neonatal outcome Highly sensitive but non-specific resulting in many unnecessary interventions.

•

Cesarean section rates had risen after introduction of CTG without major impact on neonatal outcome.

II. Intermittent Auscultations Fetal monitoring by intermittent auscultation has been shown to be equally effective to 7

electronic FHR monitoring in predicting fetal outcome with less need for cesarean sections. III. Fetal Scalp pH Testing Gold standard test of acid-base status. Management according to result: pH > 7.25 Reassuring pH < 7.2 Immediate delivery pH 7.2-7.25 Repeat after 20-30 minutes Used in only 10% of obstetric centers. Invasive, labour-intensive, require repetitions. IV. Tests of Limited Use / Unproven Value • Amnioinfusion • Vibroacoustic Stimulation • Oxygen Saturation • Scalp Lactic Acid • Fetal ECG Monitoring • ; recent promising evidence. MANAGEMENT OF ABNORMAL FHR PATTERN 3. Turn patient onto side to alleviate vena cava compression. 4. Discontinue intravenous oxytocin. 5. Apply 100% oxygen to mother by face mask. 6. Correct maternal hypertension. 7. Vaginal examination to rule out prolapsed cord. 8. Consider fetal scalp blood sampling for pH determination Search for the cause Late decelerations: excessive uterine contractions, maternal hypotension, or maternal hypoxemia. Severe variable or prolonged decelerations: Umbilical cord prolapse Rapid descent of the fetal head Cord compression 9. With decreased variability, consider fetal scalp stimulation. 10. With prolonged bradycardia unresponsive to other maneuvers or late decelerations with worsening fetal acidosis (pH <7.20), consider delivery by CS. 11. The decision to intervene depends on: o Assessment of the likelihood of severe hypoxia and the possibility of metabolic acidosis o The estimated time to spontaneous delivery.

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