Definition of fetal monitoring
- Method of assessing fetal status before and during labor
Why is fetal monitoring important?
To provide insight that may affect fetal outcome
ANTENATAL FETAL MONITORING
WHAT IS THE AIM OF MONITORING?
- To decrease perinatal morbidity & mortality
- It should guide future care
- Reassurance
- More frequent testing
- Admission to hospital
- Delivery
WHICH PATIENTS ARE EXPECTED TO BENEFIT
FROM THIS TESTING?
Patients at risk
- IUGR
- decrease fetal movement
- Post-term pregnancy > 42 wk
- Preeclampsia
- DM
- Insulin requiring GD
- PPROM
- stable abruption
INTRAPARTUM FETAL MONITORING
WHAT ARE THE METHODS AVAILABLE FOR FETAL MONITORING IN LABOR?
Electronic fetal heart monitoring --> External or internal
Intermittent auscultation
Fetal scalp sampling --> pH determination
Color of the amniotic fluid
WHAT IS THE AIM OF MONITORING ?
To decrease the risk of intrapartum fetal asphyxia
- Intrapartum fetal monitoring means simply to watch the fetal behaviour during labour.
Aim:
To detect hypoxia and so prevent asphyxia which may cause either death or permanent neurological damage as cerebral palsy, mental deficiency or both.
ANTEPARTUM FETAL MONITORING
Two thirds of fetal deaths occur before the onset of labor.
Many antepartum deaths occur in women at risk for uteroplacental insufficiency.
Ideal test: allows intervention before fetal death or damage from asphyxia.
Preferable: treat disease process and allow fetus to go to term.
Methods for antepartum fetal assessment
- Fetal movement counting
- Assessment of uterine growth
- Antepartum fetal heart rate testing
- Biophysical profile
- Doppler velocimetry
Fetal movement counting
Maternal perception of a decrease in fetal movements may be a sign of impending fetal death
3 movements in 30 minutes.
10 fetal movements noticed in 10hrs or less, the fetus must probably is in good health
Assessment of uterine growth
General rule: Symphysofundal height in centimeters after 24 weeks till 36 weeks will equal the weeks of gestation.
Exceptions: maternal obesity, multiple gestation, polyhydramnios, abnormal fetal lie, oligohydramnios, low fetal station, and fetal growth restriction.
Abnormalities of fundal height should lead to further investigation.
Antepartum fetal heart rate testing
When to begin testing
Single factors with minimal to moderate increased risk for antepartum fetal death: 32 weeks.
Highest maternal risk factors: 26 weeks.
Which test to use?
Nonstress test
Contraction stress test
Low incidence of unexpected fetal death
Increase in time, cost and inconvenience
Biophysical profile, modified biophysical profile
Doppler velocimetry
Nonstress test (NST)
The nonstress test (NST) is performed by auscultation of the fetal heart rate using an electronic monitor.
- Healthy fetuses display normal oscillations and fluctuations of the baseline FHR.
- Absence of these patterns is associated with increase in neonatal depression and perinatal mortality.
- Accelerations of the FHR during stress testing correlates with fetal well being .
- Accelerations of the FHR occur with fetal movement, uterine contractions, or in response to external stimuli.
- FHR accelerations appear to be a reflection of CNS alertness and activity.
- Absence of FHR accelerations seems to depict CNS depression caused by hypoxia, drugs, fetal sleep, or congenital anomalies.
Performing the NST
External monitors for contraction and FHR measurement applied.
Patient in left lateral tilt (to minimize supine hypotension).
Interpreting the NST
Reactive: 2 or more accelerations in 20 minutes.
Accelerations: an increase of at least 15 BPM above the baseline lasting at least 15 seconds.
Fetal stimulation by sound (vibroacaustic stimulation) may be used to elicit a response.
Interpreting the NST
Non reactive: Less than 2 accelerations in a 20-minute period.
May extend the testing period to 40 minutes or perform a back-up test.
Reactive/Nonreactive with decelerations: individualize management
Baseline FHR
Normal baseline FHR in a term fetus 37 completed weeks or more is 110-160 bpm.
Determination of the baseline FHR is done between contractions
Baseline is rounded in increments of 5 bpm example; if the FHR is running 125-135 then the baseline FHR should be documented as 130
FHR Pattern
Baseline :
1. Normal = 110 – 160 beats/min
2. Tachycardia – Moderate 160 – 180 beats/min
3. Severe > 180 beats/min
4. Bradycardia – Moderate 100 – 110 beats/min
Severe < 100 beats/min
Variability:
Normal > 5 beats/min
Reduced 3 – 5 beats/min
Absent < 3 beats/min
FHR Variability
Normal changes and fluctuations in the FHR over time.
Best assessed between contractions
Considered to be the best indicator of fetal well-being
Variability can be influenced by hypoxic events, maternal hemodynamic issues, drugs, etc.
Examples of Variability
Absent: Not detectable from baseline
Minimal: Less than 5 bpm from baseline
May occur with:
normal fetal sleep patterns
mother has received analgesia for pain
Moderate : 6-25 bpm from baseline (optimal pattern)
Marked: More than 25 bpm from baseline
How Do Uterine Contractions Affect Fetal Heart Rate?
Can affect FHR by increasing or decreasing the rate in association with any given contraction.
3 primary mechanisms by which UCs can cause a decrease in FHR are by compression of
- Fetal head
- Umbilical cord
- Uterine myometrial vessels
Periodic and Episodic FHR Characteristics
Periodic: Refers to changes in the FHR that occur with or in relationship to contractions
Episodic: Refers to changes in the FHR that occur independent of contractions
Late Deceleration
Occur in response to utero-placental insufficiency. Blood flow to the fetus is compromised and there is less oxygen available to the fetus)
Prolonged Deceleration
- Deceleration of the FHR from the baseline lasting more than 2 minutes but less than 10 minutes.
- No explanation for why these occur
- Commonly associated with uterine hyperstimulation.
- Can also occur without any uterine activity
Characteristics of Contractions
Frequency: How often they occur? They are timed from the beginning of a contraction to the beginning of the next contraction.
Regularity: Is the pattern rhythmic?
Duration: From beginning to end - How long does each contraction last?
Intensity: By palpation mild, moderate, or strong.
By IUPC (intra-uterine pressure catheters) intensity in mmHg
Subjectively: Patient description
Methods of Electronic Fetal Monitoring
External (cardiotocography)
Noninvasive method
Utilizes an ultrasonic transducer to monitor the fetal heart
Utilizes the tocodynamometer (toco) to monitor uterine contraction pattern
Methods of Electronic Fetal Monitoring
Internal Fetal Monitoring
Invasive
FHR is monitored via a fetal scalp electrode
Uterine activity is monitored by an intrauterine pressure catheter (IUPC)
ANTEPARTUM FETAL MONITORING
Contraction stress test (CST)
- Uterine contractions producing an intra-amniotic pressure in excess of 30 mm Hg, create an intra-myometrial pressure that exceeds mean intra-arterial pressure, therefore temporarily halting uterine blood flow.
- A hypoxic fetus will manifest late decelerations.
- Late decelerations correlate with stillbirth, IUGR, and low Apgar scores.
- Oxytocin challenge test (OCT))
- Breast (nipple) stimulation
External monitors for contraction and FHR measurement applied.
Patient in left lateral tilt (to minimize supine hypotension).
oxytocin infusion or breast stimulation.
Goal: three contractions in ten minutes.
- Interpretation of the CST
Suspicious: Late decelerations are present with less than half of the contractions.
Hyperstimulation: Decelerations after contractions lasting more than 90 seconds
Unsatisfactory: Cannot induce adequate contractions or FHR recording is of poor quality.
Contraindications to CST
- PROM
- Previous classical cesarean delivery
- Placenta previa
- Incompetent cervix
- History of premature labor in this pregnancy
- Multiple gestation
Biophysical profile (BPP)
The BPP is another test for the evaluation of fetal well-being . It combines the NST with the observation by ultrasound of 4 variables:
- fetal breathing movements
- fetal body movements
- fetal tone
- amniotic fluid volume
Each variable
When normal: 2
When abnormal: 0
Highest Score: 10, Lowest Score: 0
Accuracy improved by increasing the number of variables assessed.
Overall false negative rate: 0.6/1000
Fetal tone: 7.5 to 8.5 weeks
Fetal movement: 9 weeks
Fetal breathing: 20 to 21 weeks
NST: 24 to 28 weeks
Modified Biophysical Profile
The MBBP is an excellent test for evaluation of the fetal well being.
Start NST in standard manner. If a spontaneous acceleration not seen within 5 min, a single1-2sec, sound stimulation is applied in the lower abdomen with the artificial larynx. This stimulus may be repeated up to three times if necessary.
A four quadrant amniotic fluid volume is assessed by placing an ultrasound transducer perpendicular to the wall of the uterus in four abdominal quadrants and measuring the largest vertical amniotic fluid pocket. A four-quadrant sum of 5 cm or greater is considered normal.
Doppler velocimetry
The use of Doppler ultrasound for the evaluation of the fetal circulation is based on the physical principle of change in frequency of a sound wave when it is reflected by a moving object. During Doppler studies fetal and maternal vessels are interrogated with ultrasound waves .
The Doppler frequency shift caused by the moving red cells is submitted to spectrographic analysis and represented graphically as a waveform. These waveforms represent changes in the velocity of the blood flowing through the vessels.
A poor indicator of fetal compromise or adaptation to the placental abnormality but does identify patients at risk for increased perinatal mortality.
Strong association between high systolic to diastolic ratios and IUGR.
An increase in the vascular resistance of the fetoplacental unit leads to a decrease in end diastolic flow velocity or its absence in the flow velocity waveform.
Abnormal waveforms reflect the presence of a structural placental lesion.
Abnormal Doppler results require specific management protocols and intensive fetal surveillance.
Uses : plays a vital role in the diagnosis of fetal cardiac defects .
assessment of the hemodynamic responses to fetal hypoxia and anemia.
diagnosis of other non-cardiac malformations.
Doppler velocimetry of the umbilical arteries
40% of combined ventricular output is directed to the placenta by umbilical arteries.
Assessment of umbilical blood flow provides information on blood perfusion of the fetoplacental unit.
Low vascular impedance allows a continuous forward blood flow throughout the cardiac cycle
Basic Principals
The volume flow in the UAs increases with advancing gestation. The high detected in the first trimestvascular impedance er gradually decreases. It is attributed to growth of placental unit and increase in the number of the functioning vascular channels.
UMBILICAL ARTERY FLOW
characteristic saw-tooth appearance of arterial flow in one direction and continuous umbilical venous blood flow in the other.
Umbilical artery
- With advancing gestation, umbilical arterial Doppler waveforms demonstrate a progressive rise in the end-diastolic velocity and a decrease in the pulsatility index.
- Absent end diastolic flow in the UA wave forms obtain by Doppler ultrasound is important evidence of fetal compromise and demands frequent and intensive fetal surveillance .
- Reversed end diastolic flow in the UA is a sign that is shortly followed by fetal demise. Fetuses with reversed end diastolic flow in the UA are acidotic and required prompt delivery.
Uterine artery Doppler
- Doppler interrogation of the uterine arteries is usualy performed with transabdominal ultrasound .
- An important variable in the interpretation of uterine artery Doppler is the gestational age at the time the test is performed.
- Test is done before 20 weeks of gestation, the no. of false positive results is high, after 24 weeks, trophoblastic invasion has ended and false positive results will decrease.
- Abnormal uterine artery doppler wave forms indicate increase resistence in the maternal side of the placenta and their main use is as a screening tool for preeclampsia.
