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Intrapartum fetal assessment
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Intrapartum Fetal Assessment
Intrapartum Fetal Assessment done to monitor fetal well being as labor
progresses
Techniques Fetal Heart Rate Monitoring
Done in 80-90% of intrapartum assessment Fetal Scalp Blood Sampling Fetal Scalp Stimulation Vibroacoustic Stimulation Fetal Pulse Oximetry Fetal Echocardiography Intrapartum Doppler Velocimetry
Internal EFHRMFHR measured by attaching a bipolar
spiral electrode directly to the fetus Invasive(+) Ruptured BOW
Internal EFHRM
External EFHRMFHR is monitored by using external
detectors applied on the maternal abdominal wall
Ultrasound Doppler PrincipleUltrasonic waves undergo a shift in
frequency as they are reflected from the moving fetal heart valves and from pulsatile blood ejected during systole
External EFHRM
Fetal Heart Rate Patterns Baseline Fetal Heart Rate (120 – 160 bpm) Approximate mean rate rounded to increments of
5 beats/min during a 10 min tracing segment Minimum baseline duration must be at least 2
minutes Exclude period of marked FHR variability and
periodic or episodic changes (e.g acceleration or deceleration)
Fetal Heart Rate Patterns Fetal Bradycardia (<110 bpm) A rate between 110 – 119 bpm, in the absence of
other non-reassuring patterns is not usually a sign of fetal compromise (Young, et al 1976)
Etiologies: Heart block Head Compression in occiput posterior or
transverse position
Fetal Heart Rate Patterns Fetal Tachycardia (>160 bpm) In the presence of good variability, tachycardia is not a
sign of fetal distress Etiologies:
Maternal fever (most common) Fetal hypoxia Fetal HF Drugs (beta sympathomimetics) Rebound (transient) tachycardia ff a deceleration
accompanied by decreased variability
Baseline FHR Variability is an important index of cardiovascular function
and appears to be regulated largely by the autonomic nervous system
Irregular fluctuations in the baseline FHR Regulated largely by the autonomic nervous
system (sympathetic & parasympathetic “push-pull” mediated via the sinoatrial node, produces beat-to-beat oscillation of the baseline FHR)
2 Types of Variability Short- Term Variability reflects the instantaneous change in FHR from
one beat or R wave to the next measure of time interval between cardiac
systoles beat to beat changes
2 Types of Variability Long-Term Variability the oscillatory changes that occur during the
course of 1 minute and result in the waviness of the baseline
Normal frequency: 3-5 cycles/min
Grades of FluctuationAbsent variability
amplitude range undetectable; flat Ominous
Minimal <5 bpm secondary to fetal sleep or drugs
Moderate 6 to 25 bpm normal
Marked > 25 bpm
Variability persistently minimal or absent FHR variability
appears to be the most significant intrapartum sign of fetal compromise
During antepartum assessment, the indicator for fetal well-being are accelerations, here in intraprtum assessment, it is variability.
on the other hand, the presence of good FHR variability may not always be predictive of a good outcome
Etiologies Fetal metabolic acidosis CNS depressants (anesthesia, anti-seizure
drugs, etc) Fetal sleep cycles Congenital anomalies Prematurity Fetal tachy Pre-existing neurologic abnormality
Acceleration an abrupt increase in FHR above baseline with
onset to peak of the acceleration less than 30 sec and less than 2 min in duration
adequate accelerations are defined as: <32 wks ≥10 bpm above baseline for ≥10
sec >32wks ≥15 bpm above baseline for ≥ 15
sec
Deceleration an abrupt increase in FHR above baseline with
onset to peak of the acceleration less than 30 sec and less than 2 min in duration
adequate accelerations are defined as: <32 wks ≥10 bpm above baseline for ≥10
sec >32wks ≥15 bpm above baseline for ≥ 15
sec
3 Types of Deceleration Early decelerationsVariable decelerationsLate decelerations
3 Types of Deceleration Early decelerationsVariable decelerationsLate decelerations
Early Deceleration Gradual decrease in FHR with onset of deceleration to nadir in
≥ 30 sec Exact mirror image of uterine contraction Same timing with uterine contraction Gradual decline
The nadir occurs with the peak of a contraction head compression probably causes vagal nerve activation as
a result of dural stimulation and that mediates the heart rate deceleration
not associated with fetal hypoxia, acidemia or low APGAR scores
typically occur during the 2nd stage of labor
Late Deceleration Smooth and gradual decrease in FHR with onset of
deceleration to nadir ≥ 30 sec Onset of the deceleration occurs after the beginning of the
contraction, and the nadir of the deceleration occurs after the peak of the contraction
Etiologies: Excessive uterine contractions (hyperstimulation), maternal
hypotension (by epidural anesthesia) or maternal hypoxemia Reduced placental exchange/ placental dysfunction as in
hypertensive disorders, diabetes, collagen vascular disorders, IUGR, abruption
Uteroplacental insufficiency
Management of Late Deceleration place patient on side (left)
to release the pressure from the major vessel (aorta)
administer 02 by tight face mask or nasal prong discontinue oxytocin- you might have triggered
hyperstimulation correct any hypotension IV hydration if hyperstimulation is present, consider terbutaline
0.25 mg SC
Variable Deceleration from the most recently determined baseline rate the onset of deceleration to nadir is less than 30 sec the deceleration lasts ≥ 15 sec and < 2 minutes pure variables are uncommonly associated with adverse fetal outcome UMBILICAL CORD OCCLUSION (e.g. Nuchal cord or cord prolapse) Features: “shouldering” Initial shallow acceleration
due to occlusion of umbilical vein Sudden Deceleration
Umbilical artery Late acceleration
Compensatory increase in heart rate
Other Fetal Heart Rate Patterns
Saltatory Pattern also associated with cord compression marked variability consists of rapidly recurring couplets of
acceleration and deceleration causing relatively large oscillations of the baseline FHR
Lambda Pattern an acceleration followed by a variable
deceleration with no acceleration at the end of deceleration – no shouldering
not ominous seen in early labor may result from mild cord compression or stretch
Overshoot variable deceleration followed by prolonged
acceleration indicates an abnormal cord position
Prolonged Deceleration an isolated deceleration lasting for 2 min or longer
but less than 10 min from onset to return to baseline
Etiologies: cervical exam uterine hyperactivity cord entanglement maternal supine hypotension epidural anesthesia maternal valsalva
FHR Patters During the 2nd Stage of Labor
Deccelerations are virtually present most of the time during the 2nd stage of labor, with both cord compression and head compression implicated as causes
Abnormal baseline FHR- either bradycardia or tachycardia, absent beat-to-beat variability, or both- in the presence of 2nd stage deceleration is associated with increased fetal compromise
Fetal Scalp Blood Sampling
an intrapartum procedure for the evaluation of fetal acid base status
by determining the pH in capillary scalp blood, fetus in serious distress may be identified
procedure is now used uncommonly
Fetal Scalp Blood Sampling
this procedure is performed only in select cases of deliveries in which the FHR raise some concern regarding fetal status but not enough to mandate immediate delivery
pH of fetal capillary scalp blood is usually lower than that of umbilical venous blood and approaches that of umbilical artery
Fetal Scalp Blood Sampling
a confusing / non-reassuring FHR pattern is present (may be subjective: get the pH if the baby is acidotic or not)
variability ≤ 5 bpm with / without periodic changes or if absent variability
mixed deceleration pattern which complicates interpretation
Contraindications
mother known carrier of hemophilia and fetus either affected or of unknown status
mother is HIV seropositive active maternal genital infection e.g. herpes
Interpretation> 7.25 labor is observed, repeat FSBS every
2-3 hours
7.20 – 7.25
repeat FSBS within 30 min
< 7.20 repeat FSBS immediately while preparing for surgery, if confirmed, delivery is indicated.
Procedure An illuminated endoscope is inserted through the dilated
cervix after ruptured membranes so as to press firmly against fetal scalp
The skin is wiped clean with a cotton swab and coated with a silicone gel to cause the blood to accumulate as discrete globules
An incision is made through the skin to a depth of 2 mm with a special blade on a long handle
As a drop of blood forms on the surface, it is immediately collected into a heparinized glass capillary tube
pH of blood is measured promptly
Fetal Scalp Stimulation
Clark, 1984 acceleration of FHR in response to pinching with
an Allis clamp was associated with normal pH however, failure to provoke acceleration was not
uniformly predictive of fetal acidemia
Fetal Scalp Stimulation
Elimian, 1997 presence of acceleration following the gentle
digital stroking revealed scalp pH ≥ 7.20 without acceleration, however, only 30% has a
scalp pH <7.20
Vibroacoustic Stimulation
use of sound to stimulate/startle the baby involves the use of an electronic artificial larynx
(or a bell) placed a cm or so from or directly onto the maternal abdomen
response is considered normal if FHR acceleration occurs within 15 sec after stimulation and with prolonged fetal movements
effective predictor of fetal acidosis in the setting of variable decelerations
Fetal Pulse Oximetry
a unique pad-like sensor is inserted through the cervix and positioned against the fetal face, where it is held by the uterine wall
the lower limit for normal fetal oxygen saturation is 30%
saturation values below 30%, when persistent for 2 min or longer, are associated with an increased risk of potential fetal compromise
Fetal Electrocardiography
Involves ST segment of the fetal ECG is analyzed, because changes occurs as fetal hypoxia worsens
Techniques requires internal monitoring of the FHR and a special equipment to process the fetal ECG
ST abnormalities may occur late in the course of fetal jeopardy
Intrapartum Doppler Velocimetry
Doppler analysis of the umbilical artery Ultrasound needs to be done in order to locate
umbilical artery Poor predictor of adverse perinatal outcomes Little role in the surveillance of fetal well-being
during labor; rarely done
Fetal Distress
Reassuring FHR pattern – suggests a restoration of confidence by a particular pattern
Non-reassuring FHR pattern – suggests inability to remove doubt
NICHD Research Planning Workshop (2008) FHR PatternsPattern Workshop InterpretationsCategory I:NORMAL
Baseline: 110 – 160 bpm (120 in the book)Variability: 6 – 25 bpm (moderate)Accelerations: Present or AbsentLate or Variable Decelerations: AbsentEarly Decelerations: Present or Absent
Category II:INDETERMINATE
Include all FHR tracings not categorized as Category I or III
Category III:ABNORMAL-non-reassuring
Include either:- Absent Baseline FHR variability and any of the following: Recurrent late decelerations Recurrent variable decelerations Shift of baseline to bradycardia- Sinusoidal Pattern
Meconium in the Amniotic Fluid
Obstetrical teaching throughout the past century has included the concept that meconium passage is a potential warning of fetal asphyxia
Not necessarily a warning that the fetus is asphyxiated Nathan, 1994 – Meconium is a “low-risk obstetrical
hazard” - perinatal mortality attributed to meconium was 1 death per 1000 live births
Meconium passage is a result of relaxation of the sphincter ani muscle induced by faulty aeration of fetal blood
Theories of Fetal Passage of Meconium
Fetuses pass meconium in response to hypoxia and that meconium therefore signals fetal compromise (Walker, 1953)
In utero passage of meconium may represent normal gastrointestinal tract maturation under neural control (Matthews & Warsaw, 1979)
Could follow vagal stimulation from a common but transient umbilical cord entrapment ad resultant increased peristalsis, thus fetal release of meconium also could represent physiological process (Hon, 1961)
Meconium Aspiration Syndrome
was significantly associated with fetal acidemia at birth
Other significant correlates of aspiration: CS forceps to expedite delivery intrapartum heart rate abnormalities depressed APGAR score need for assisted ventilation at delivery
Meconium Aspiration Syndrome
Meconium in amniotic fluid is a fetal environmental hazard (when acidemia supervenes) rather than a marker of a preexistent compromise.
Fetal hypercarbia/acidemia → stimulates fetal respiration → aspiration of meconium, into the alveoli → lung parenchymal injury (Ramin, 1996)
Management Options of Fetal Distress
1. Tocolysis Terbutaline sulfate 1.25 mg IV or SQ single dose –
uterine relaxant Temporizing maneuver to relax the uterus and
improve fetal oxygenation, prior to CS
Management Options of Fetal Distress
2. Amnioinfusion (transvaginal) For oligohydramnios For meconium stained amniotic fluid 500-800 ml bolus of warmed normal saline
followed by a continuous infusion of approximately 3 ml per min
Intrapartum Surveillance of Uterine Activity
Internal Uterine Pressure Monitoring Contractions occurring within 3 minutes, whether mild,
moderate or strong, you should record it. amniotic fluid pressure is measured between and during
contractions by a fluid-filled plastic catheter with its distal tip located above the presenting part
the catheter is connected to a strain-gauge pressure sensor adjusted to the same level as the catheter tip in the uterus
the amplified electrical signal produced in the strain gauge is recorded on a calibrated moving paper strip simultaneously with the fetal heart rate recording
External Monitoring
uterine contractions can be monitored by a displacement transducer in which the transducer button or plunger is held against the abdominal wall (at the fundus)
it does not give an accurate measure of intensity but only the relative intensity (not as accurate as putting a catheter inside the uterine cavity above the presenting part)
but can give a good indication of the onset, peak and end of contraction
Montivideo Units
Used to measure the units of uterine contraction during labor
Direct measure of the pressure of uterine contractions
Uterine performance is the product of the intensity of a contraction in mmHg x contraction frequency per 10 min
Get the amplitude x 3 u.c./10min
Montivideo Units
Labor usually commences when uterine activity reaches values between 80 & 120 Montevideo units (~3 contractions / 10 min with an intensity of 40 mmHg)
No clear cut division
Montivideo Units
First stage of labor Intensity: 25-50 mmHg Frequency: 3-5 u.c. / 10 min
Second stage (full dilatation) Intensity: 80-100 mmHg Frequency: 5-6 u.c. / 10 min (every 2 minutes) Duration: 60-80 sec, constant from 1st stage to 2nd stage
Origin and Propagation of Contractions10 mmHg palpable contractions
<40 mmHg uterine wall can be readily depressed (mild to moderate)
>40 mmHg Uterine wall can no longer be readily depressed/indented (contraction is at its peak)
>15 mmHg pain can be appreciated, the minimum pressure required for distending the lower uterine segment and cervix
Origin and Propagation of Contractions
the normal contraction wave of labor originates near the uterine end of one of the fallopian tubes - “pacemakers”
the right pacemaker dominates over the left and starts the great majority of contractile waves
contractions spread from the pacemaker area throughout the uterus at 2 cm/sec, depolarizing the whole uterus within 15 sec
the depolarizing wave propagates downward toward the cervix
Summary
FHR patterns that you should be able to determine in a strip: Baseline FHR
2 mins Without any accelerations or decelerations N: 120-160 Bradycardia: <110 Tachycardia:> 160
Summary
Variability Absent Minimal: <5 Normal: 6-25 Marked: >25
Uterine hyperstimulation
Summary
Accelerations <32 wks ≥10 bpm above baseline for ≥10 sec >32wks ≥15 bpm above baseline for ≥ 15 sec
Summary
Decelerations Episodic
unrelated to uterine contractions Periodic
associated with uterine contractions
Summary
Early associated with head compression; lowest FHR corresponds with peak of uterine contraction,
creating a mirror-imag not associated with fetal hypoxia, acidemia, low APGAR
Summary
Late uteroplacental insufficiency lowest heartbeat occurs after the peak of uterine
contraction fetal hypoxia
Summary
Variable cord compression uncommonly associated with adverse fetal outcome, unless
with pathologic features sharp (compared to the others, which are gradual) decrease
in fetal heartbeat unrelated to uterine contraction
Summary
Fetal scalp blood sampling: N: >7.25 < 7.20 – acidosis is suspected
Scalp stimulation and vibroacoustic stimulation should cause FHR acceleration
Pulse oximetry: N: 30% O2 sat
Summary
Meconium staining: May be pathologic, but most of the time
physiologic Watch for occurrence of meconium aspiration
acute or unpredictable check the fetal vocal cords if there is meconium - if
none, baby is ok; if meconium-stained, suspect meconium- aspiration
Summary
Amnioinfusion To correct oligohydramnios, thus improving FHR
pattern Not recommended in meconium-stained
amniotic fluid because you may be increasing the environmental hazard characteristic of the meconium, which may cause meconium aspiration
Summary
Montevideo unit Uterine pressure x # of contraction/ 10 min
Uterine pacemaker near the uterine end of the fallopian tube right dominating the left propagate at 2 cm/s towards the cervix
Electronic Fetal HR Monitoring Internal EFHRM External EFHRM