PRINCIPLES OF FETAL MONITORING

May, 2010

Dr. Nagat Salah

Why do we monitor the fetus?

Monitoring is one method used to determine the fetus’ well being and to assess labor progress. During labor, it is used to assess the baby’s reaction to contractions and tolerance of labor.

Many patients require continuous monitoring because of medication they are receiving or health concerns related to themselves or their unborn baby. Some patients who are low risk may need only intermittent monitoring.

Ways of antenatal assessment of fetal growth Clinical Chemical Biophysical

Clinical

Uterine size Maternal weight gain

Chemical Fetoplacental hormone Placental hormones Placental proteins

Biophysical methods Counting of fetal movements Non stress test Contraction stress test Electronic fetal monitoring sonography

Non stress test Evaluation of the fetal heart rate

response to fetal movement. It is used to identify fetal compromise in conditions associated with poor placental function

The expected response is an acceleration of 15 b/min lasting 15 sec. with at least two fetal movement (must be done each visit from 30 wk

The reactive test is present when2 or more fetal heart rate acceleration are clearly recorded during 20 min. each acceleration of 15 or more b/m

If there is no acceleration during 40.min. the test considered non reactive

Contraction stress test The idea: evaluation of fetal heart

rate in response to mild uterine contraction.

Contraction may be induced by self stimulation of the nipples or by intravenous oxytocine

Biophysical profilevariable Score 2 Score 0

Fetal breathing movement (FBM)

The presence of at least 30 second of sustained FBM in 30 minutes of observation

Less than 30 seconds of FBM in 30 min.

Fetal movement Three or more gross body movement in 30 min.

Two or less gross body movements in 30 min. of observation

Fetal tone At lest on episode of motion of a limb from a position of flexion to extension and a rapid return to flexion

In a position of semi- or- full limb extension with movement. Or absence movement

Fetal activity Presence of two or more FHR acceleration of 15b/m lasting 15 seconds

No acceleration or less than two acceleration

Qualitative amniotic volume

A pocket of amniotic fluid measure at least I cm in two perpendicular planes

Largest pocket of amniotic fluid measure less thanI cm in two perpendicular planes

Maximum score 10 -

The electronic fetal monitor (EFM) is a device that records an unborn baby's heart rate and the presence or absence of the mother's uterine contractions.

The monitor produces a continuous paper record of the fetal heart rate (FHR) and records uterine contractions.

Electronic Fetal Monitor

Electronic fetal monitoring can be performed with monitors outside the body (external monitoring) or in the uterus (internal monitoring). 

About Electronic Fetal Monitoring

External Fetal Monitoring

How do external monitors work?

The ultrasound transducer (ultrasound) is attached to the abdomen with straps and transmits the fetal heartbeat to a recorder. Gel on the mother’s abdomen acts as a medium or conductant for the ultrasound transducer.

How do external monitors work? (Continued)

A tocodynamometer or tocotransducer (toco) is a monitoring device that is placed over the top of the uterus with a belt.

As the patient’s abdomen tightens during a contraction, it presses against a sensor on the back of the toco. This registers as an upward deflection on the monitor paper. As the patient’s abdomen relaxes, the pressure against the sensor decreases, which registers as a downward deflection on the paper.

Determining where the monitors go

To determine where the monitors should be applied, you need to determine which way the baby is facing and whether the baby is head down (cephalic or vertex) or head up (breech).

Among its other purposes, Leopold Maneuver’s is a multi step process to obtain information about the fetus’s position. Knowing this information will help you know where to place the monitors and belts.

Placing the Ultrasound Transducer

•Place patient in semi or low fowler’s position

•Apply ultrasound gel to backside (usually white or light grey) of transducer

•Place the transducer over the fetal back. It will be below the umbilicus for a term fetus, who is head down (vertex) and adjacent to or above the umbilicus for a fetus who is breech.

Placing the ultrasound transducer (Continued)?

•Secure the transducer in place with belts after observing that the signal is being recorded on the electronic fetal monitor. The green light will flash with every heart beat.

•If the signal is not clear or is lost, apply additional gel to the back side of the transducer, if necessary, and reposition the transducer on the patient’s abdomen.

Placing the tocotransducer(toco)

Place the monitor belt around the patient’s abdomen

Place the tocotransducer on the patient’s abdomen over the upper uterine segment, approximately 2 cm from the top of the fundus

Secure tocotransducer with the monitor belt

If your patient is preterm, she may report feeling contractions in a lower area of her abdomen. Palpate the patient’s abdomen. You may wish to place the tocotransducer in this area if you feel or suspect contractions are present.

When is internal fetal monitoring used?

Common reasons for using internal monitors are:

•the baby is difficult to keep on the monitor

•the baby has an abnormal heart rate or is having decelerations in its heart rate

•the patient is having contractions but accurate information as to their actual strength is needed to determine whether the patient needs oxytocin to make them stronger and more effective

Internal Fetal Monitoring

How do internal monitors work?

There are two types of internal monitors - a fetal scalp electrode and an intrauterine pressure catheter (IUPC). They are only used once the patient’s "water has broken" and her cervix has dilated enough.

A fetal scalp electrode is a device that monitors the baby’s heart rate. It consists of a small clip that is placed on the baby’s scalp. The electrode is attached to a cable.

Intrauterine pressure catheter (IUPC) is a small catheter that is placed up into the patient’s uterus. It goes between the uterine wall and the baby. It directly measures the strength of her contractions and resting tone in millimeters of Hg. It provides more accurate information as to the strength of contractions than an external monitor (tocodynameter).

How do internal monitors work? (continued)

An IUPC can also be used to instill an amnioinfusion.

Internal Fetal MonitoringIntrauterine Pressure Catheter

Cardiotachometer

Fetal Scalp Electrode

What information is recorded on the electronic fetal monitor?

The fetal heart rate and uterine contractions are recorded on the fetal monitoring strip.

Also, maternal vital signs (blood pressure, pulse, respirations and oxygen saturation) are recorded.

Further, the time and date of the recording are indicated on the strip and whether you are using internal monitors or external monitors.

Fetal Heart Rate Paper

Date

Time

Paper speed in North American is 3 cm/minute. There are six (6) in one minute between the dark lines so each little box represents ten (10) seconds.

Dark red lines are one minute apart

Maternal vital signs

Scale: Fetal Heart Rate

Fetal heart rate in ten beat intervals ranging from 30 beats per minute to 240 beats per minute. Normal fetal heart rate is 120 to 160 beats per minute

•In 1997, the National Institute of Child Health and Human Development (NICHD) Research Planning Workshop published guidelines for the interpretation of fetal tracings.

•Under these guidelines, standardized definitions of fetal heart patterns were developed.

•This terminology is used by AWHONN (Association of Women’s Health Obstetric and Neonatal Nurses)

Fetal Heart Rate Interpretation: Definitions

Fetal Compromise Inadequate oxygen causes fetal hypoxemiahypoxemia Fetal hypoxemia causes tissue hypoxiatissue hypoxia Tissue hypoxia results in anaerobic anaerobic

metabolismmetabolism Anaerobic metabolism causes production of

lactic acidlactic acid Lactic acid causes

metabolic acidosismetabolic acidosis shunting of blood to vital organs (heart, brain, shunting of blood to vital organs (heart, brain,

adrenalsadrenals)

Basic Warning Signs Contractions lasting longer than 90

seconds Relaxation between contractions of

less than 60 seconds Resting uterine tone above 20 mmHg Peak pressure of contractions above

90 mmHg (except in second stage)

Basal Fetal Heart Rate Normal Fetal Heart Rate at Term:

120-160 beats per minute until week 26 the fetal heart rate is

controlled by the sympathetic nervous system

as the fetus matures the parasympathetic nervous system increases as a control

parasympathetic control = vagus nerve vagal stimulation slows the heart

1. Evaluate tracing. Do you have enough of a continuous strip for interpretation?

2. Identify fetal heart rate baseline

3.Identify existence and degree of variability (absent, minimal, moderate or marked)

4. Determine whether there are accelerations or decelerations.

5. Evaluate pattern of uterine contractions.

Steps in Interpreting a Fetal Heart Rate Tracing

Steps in Interpreting a Fetal Heart Rate Tracing (Continued)

6. Identify regularity, rate, intensity, duration of contractions.

7. Correlate accelerations and decelerations with uterine contractions and identify the pattern.

8. Determine whether the FHR recording is reassuring, nonreassuring or ominous.

9. Document interpretation of FHR, clinical conclusion and plan of care. Notify physician or midwife as appropriate.

Interpreting Fetal Heart Rate

To establish fetal heart rate baseline, determine the approximate mean FHR rounded to increments of 5 beats/min in a 10-minute segment of tracing, excluding periodic or episodic changes, periods of marked variability, and segments of baseline that differ by >25 beats/min.

Determining the Baseline

In any ten minute segment of fetal monitoring strip, the minimum baseline duration is two minutes within the ten minute segment.

Above, the baseline is 130 beats per minute. Each red line indicates a two minute (12 boxes) segment of baseline.

What if there is no clear fetal heart rate baseline?

Sometimes the fetal heart rate will vary so much over a ten minute period that you may not have a two minute minimum portion of the tracing upon which to determine the fetal heart baseline.

Under this circumstance, the baseline is noted as being “indeterminate.”

Describing Fetal Heart Rate

Fetal heart rate is described in terms the number of beats per minute (bpm) and whether the rate is normal, faster than normal or slower than normal.

Normal fetal heart rate is 120-160 bpm.

Fetal tachycardia is a baseline of over 160 bpm.

Fetal bradycardia is a baseline under 120 bpm.

What is baseline variability?

The term “variability” refers to fluctuations in the fetal heart rate of more than two cycles per minute.

These fluctuations are irregular in amplitude and frequency. The distance between the highest point and the lowest point of each of the fluctuation is referred to as “amplitude.”

Changes in the fetal heart rate are due to the interaction of the sympathetic and parasympathetic systems of the fetus.

Baseline Variability

Absent: Amplitude range is undetectable

Minimal: Amplitude range is less than 5 beats/minuteor fewer

Moderate: Amplitude range is 6

to 25 beats/minute

Marked: Amplitude range is >25 beats/minute

Short-Term Variability Significance: below 5 beats/min may

indicate: fetal sleep period (intermittent periods) CNS depression prematurity - immature parasympathetic

system hypoxia - stimulates the vagus nerve which

slows the heart, decreases variability drugs - analgesics, sedatives, anesthetics maternal smoking

Response to Decreased STV Stimulate fetus (wake up!) Attach scalp electrode: variability

is better seen on internal monitor Check fetal pH Oxygen IV fluids Change maternal position

Long-Term Variability Variability in the baseline rate over

a more extended period of time (one minute) usually 3-10 cycles/minute amplitude of 3-25 bpm decreased during sleep, drugs,

hypoxia, tachycardia increased during hypoxia

Response to Decreased LTV Stimulate fetus Internal monitor Fetal pH Oxygen Change maternal position IV fluids

Predictable Events Head Compression Uteroplacental Insufficiency Cord Compression

Fetal Tachycardia

Fetal heart rate above 160 beats per minute

Fetal tachycardia with fetal arrhythmia

Common Causes of Fetal Tachycardia

Maternal fever/infection (Amnionitis)

Fetal hypoxia

Anticholinergic drugs, e.g. Atropine

Betasympathomimetic drugs, e.g.. Terbutaline

Maternal illicit drug use, e.g.. Cocaine, Methylamphetamines

Maternal anxiety

Fetal anemia

Certain fetal cardiac arrhythmias

Fetal Bradycardia

Baseline fetal heart rate less than 110 beats per minute

Prolonged cord compression

Cord prolapse

Tetanic uterine contractions

Paracervical block

Epidural and spinal anesthesia

Maternal seizures

Rapid descent

Vigorous vaginal examination

Common Causes of Fetal Bradycardia

An acceleration is an abrupt increase in FHR above baseline with onset to peak of the acceleration less than 30 seconds and less than 2 minutes in duration.

The duration of the acceleration is defined as the time from the initial change in heart rate from the baseline to the time of return to the FHR to baseline.

Accelerations

Adequate accelerations are defined as:

>32 weeks' : >15 BPM above baseline for > 15 seconds, but less than 2 minutes

Accelerations: >32 weeks

For under 32 weeks, accelerations are defined as : >10 BPM above baseline for > 10seconds, lasting less than two minutes.

The tracing of a premature fetus, especially before 28 weeks, typically will have a higher fetal heart rate baseline, and exhibit less variability and lower amplitude accelerations than a fetus over 32 weeks.

Accelerations: <32 weeks

Increase in fetal heart rate lasts for 2 minutes or more, but less than 10 minutes

Any apparent acceleration that lasts longer than 10 minutes is considered to be a change in the fetal heart baseline.

Prolonged Acceleration

Periodic vs. Episodic Changes

Periodic changes: These are accelerations or decelerations in the fetal heart rate that occur in direct association with uterine contractions.Episodic changes: These are accelerations or decelerations in the fetal heart rate that occur independent of uterine contractions. (ex. A deceleration or acceleration in response to a vaginal exam, maternal vomiting, or fetal movement)

Periodic vs. Episodic Changes (Continued)

Periodic change- variables associated with each contraction

Nonperiodic change- prolonged deceleration

An abrupt  decrease in FHR of > 15 beats per minute measured from the most recently determined baseline rate.  The onset of deceleration to nadir is less than 30 seconds. The deceleration lasts   > 15 seconds and less than 2 minutes.

Variable Deceleration:

Cause of Variables

Variables are transitory decreases in the fetal heart rate caused by umbilical cord compression. They coincide with contractions. They may be v-shaped, u-shaped or w-shaped.

The significance of the variables depends upon how often they occur, how deep they go and how long they last. What also is crucial is how the fetus responds in their presence.

Variable Shapes

V-shaped

U-shaped W-shaped

Head Compression

As the uterus contracts it compresses the engaged head vagal slowing

Causes an “Early Deceleration” deceleration starts and ends with uterine

contraction pattern is symmetrical NOT considered a sign of distress

Early Decelerations

In association with a uterine contraction, a visually apparent, gradual (onset to nadir 30 seconds or more) decrease in FHR with return to baseline.

Nadir of the deceleration occurs at the same time as the peak of the contraction.

Early Decelerations

Early deceleration is caused by vagal simulation from head compression, and is a reassuring pattern that may be prevented by avoiding early rupture of membranes.

Early decelerations are not considered ominous.

Late Decelerations

In association with a uterine contraction, a visually apparent, gradual (onset to nadir 30 seconds or more) decrease in FHR with return to baseline. Onset, nadir and recovery of the deceleration occur after the beginning, peak and end of the contraction.

Late deceleration is associated with uteroplacental insufficiency and is a result of hypoxia and metabolic abnormalities. Late decelerations are one of the most ominous fetal heart rate patterns!

Late Deceleration

Response to Late Decelerations “Non-Reassuring” (Bad stuff is happening) Change maternal position to side (supine

position compresses maternal aorta and vena cava)

Stop oxytocin (pitocin contracts the uterus, impedes blood flow/oxygen exchange)

Increase IV fluids (correct hypotension) Oxygen (up to 100%)

A decrease in FHR of > 15 beats per minute measured from the most recently determined baseline rate. The deceleration lasts >= 2 minutes but less than 10 minutes.  

Prolonged Decelerations

Prolonged deceleration following uterine rupture

Prolonged deceleration following vaginal exam: vagal

• Maternal hypotension

• Uterine hyperactivity

• Cord prolapse

• Cord compression

• Abruption

• Uterine rupture

Common Causes of Prolonged Deceleration

•Fetal hypoxia

•Fetal hemorrhage

•Maternal hypoxia

•Fetal vagal

Cord Compression

Fetal heart rate deceleration is variable in shape, onset, non-repetitive

Most common type of deceleration Caused by cord compression

compressed cord causes increased BP baroreceptors cause bradycardia if prolonged, hypoxia

Response to Variable Decelerations Change maternal position to right or

left side, or Trendelenburg Elevate presenting part (lift off cord) 100% oxygen Stop oxytocin Persistent Bradycardia: Deliver

forceps (if delivery imminent) or C-section (if delivery is not imminent)

Sinusoidal Pattern

This is a rare, but ominous pattern, which is associated with a high rate of fetal death. It consists of an undulating form of sine wave that is regular, smooth and undulating. It repeats two to five cycles per minute and has an amplitude range of five to 15 beats per minute. No fetal accelerations.

Common Causes of Sinusoidal Pattern

Fetal Anemia associated with:

•Rh isoimmunization

•Fetal hypoxia

•Chronic fetal bleeds

•Fetal-maternal hemorrhage

•Severe acidosis

What is a reassuring fetal heart tracing?

In labor, fetal heart rate patterns are called reassuring, nonreassuring or ominous. Reassuring patterns are associated with fetal well-being and positive outcomes.

Reassuring patterns:

Mild variable decelerations (less than 30 seconds in duration with rapid return to baseline)

•Early decelerations (concurrent "mirror image" decrease with contraction)

• Accelerations without other changes

An increase of 15 beats per minute above the baseline for 15 second duration (from baseline to baseline) twice in a 20 minute period. 

What makes a strip reassuring?

Only 65% of fetuses at 28 weeks are reactive. By 34 weeks 95% of fetuses are reactive. 

What is a nonreassuring strip?

Fetal tachycardia

Fetal bradycardia

Late Decelerations

Variable decelerations with nonreassuring pattern

What is an ominous pattern?

Recurrent late decelerations with loss of variability

Variable decelerations with loss of variability

Prolonged bradycardia

Sinusoidal pattern

Loss of variability not associated with fetal sleep cycle, medications, or fetal prematurity

STIMULATE THE FETUS CHANGE THE MATERNAL POSITION INCREASE IV GIVE OXYGEN STOP OXYTOCIN

                                                                                                                            

                                                                                                                  

                                                                                                                            

                                                                                                                  

Thank you

Scale: Contractions

Uterine Activity

Measured in 0 to 100 mm/Hg

How to Interpret Contractions

The duration in seconds of a contraction is measured by counting the number of boxes in between the start of the contraction and the end of the contraction and multiplying this number by 10. The frequency is determined by measuring the time between the start of one contraction until the start of another contraction

Strength of a Contraction

When using an external monitor (tocodynameter) , remember that the actual strength of contraction is subjective

To determine, palpate the patient’s abdomen during a contraction- a poor contraction feels like your cheek or the tip of your nose, a moderate contraction feels like your chin, a strong contraction feels like your forehead

Strength of a Contraction (Continued)

When a patient has an IUPC, the strength of contractions can be calculated in units called “Montevideo units.”

Units are calculated by measuring uterine pressure above baseline tone and multiplying by the number of contractions in a 10 minute period.

Calculating Montevideo Units

For example, uterine pressure above baseline were 60 mmHg, and during the 10 minute period of measurement 3 contractions occurred, total Montevideo units (MVUs) would be equal to 180 MVUs. Generally, above 200 MVUs is considered necessary for adequate labor during the active phase.