Methods of Monitoring The Fetal Heart Rate:(1) Fetal Stethoscope (Pinard) and Hand-Held Doppler (Sonicaid)(2) Cardiotocograph (CTG)
(1) Fetal Stethoscope (Pinard) and Hand-Held Doppler:• Intermittent monitoring can be undertaken either by listening to: 1. the baby’s heart rate using a fetal stethoscope (Pinard) - after French obstetrician Adolphe Pinard or 2. a handheld doppler ultrasound device and 3. by palpating the mother’s uterine contractions by hand. This is known as ’intermittent auscultation
(2) Cardiotocography (CTG)• Cardiotocography (CTG) is a technical means of recording (-graphy) the fetal heartbeat (cardio-) and the uterine contractions (-toco-) during pregnancy, typically in the third trimester.• The machine used to perform the monitoring is called a Cardiotocograph, more commonly known as an Electronic Fetal Monitor (EFM).
Note• The term Electronic Fetal Monitoring is sometimes used instead of CTG monitoring, but is considered to be a less precise term because :1. CTG monitoring also includes monitoring the mother’s contractions and2. other forms of fetal monitoring might also be classed as ‘electronic’ e.g. ECG, fetal pulse oximetry
Method• Recordings are performed by TWO separate transducers; one for the measurement of the fetal heart rate and a second one for the uterine contractions.• Each of the transducers may be either external or internal. 1) External measurement means taping or strapping the two sensors to the abdominal wall. This is called an indirect measure
2) Internal measurement ( direct ) requires a certain degree of cervical dilatation, as it involves inserting a pressure catheter into the uterine cavity, as well as attaching a scalp electrode to the childs head to adequately measure the electric activity of the fetal heart. Internal measurement is more precise, and might be preferable when a complicated childbirth is expected.
Interpretation• Includes description of: 1) Uterine activity (contractions) 2) Baseline fetal heart rate 3) Baseline FHR variability 4) Presence of accelerations 5) Periodic or episodic decelerations
1) Uterine Contractions• There are several factors used in assessing uterine activity :a) Frequency: the amount of time between the start of one contraction to the start of the next contraction.b) Duration: the amount of time from the start of a contraction to the end of the same contraction. (e.g. 15 secs)c) Intensity: a measure of how strong a contraction is. (mild, moderate, strong)
Intensity• With external monitoring, this necessitates the use of palpation to determine relative strength.• With internal monitoring, this is determined by assessing actual pressures as graphed on the paper.
d) Resting Tone: a measure of how relaxed the uterus is between contractions.e) Interval: the amount of time between the end of one contraction to the beginning of the next contraction.
Uterine Activity• May be defined as: Normal less than or equal to 5 contractions in 10 minutes. Tachysystole more than 5 contractions in 10 minutes .
2) Baseline Fetal Heart Rate• The average rate between peaks and depressions over a period of time that doesn’t include accelerations or decelerations of the heart rate.• The baseline fetal heart rate is the heart rate range that occurs between uterine contractions.• The normal baseline heart rate can be anywhere between 110 and 160 beats per minute.
How Do Uterine Contractions Affect Fetal Heart Rate?• Uterine contractions can affect fetal heart rate by increasing or decreasing that rate in association with any given contraction.• The THREE primary mechanisms by which uterine contractions can cause a decrease in fetal heart rate are compression of: o Fetal head o Umbilical cord o Uterine myometrial vessels
• With each contraction, blood flow from the mother to the baby initially ceases as the uterine myometrial veins are compressed.• At this point, the mother and baby are physiologically separated from each other for a few seconds.• As the contraction begins to subside, the uterine myometrial arteries re-open, allowing blood carrying oxygen and nutrients to flow from the mother to the baby, and the uterine myometrial veins reopen, allowing blood carrying fetal waste products to flow from the baby to the mother.
What are Causes of Fetal Heart Rate Bradycardia?• Fetal bradycardia is defined as a decrease in the baseline FHR to less than 100 beats per minute1. Fetal Hypoxia: Bradycardia is a late sign of fetal hypoxia (a continual lack of oxygen). o The heart rate slows in response to a depression of heart muscle (myocardial) activity caused by this continued decrease in needed oxygen.2. Medications: Medications such as narcotics cause bradycardia by preventing receptor sites in the fetal heart muscle from accepting epinephrine, which works to increase heart rate.
3. Epidurals: cause vasodilation, which leads to an increase in the incidence of maternal hypotension during labor WHICH causes bradycardia indirectly due to a reflex mechanism, a potential complication for regional anesthesia. o Anesthetic medications can produce bradycardia approximately 5 minutes following the block. The heart rate then usually returns to normal baseline rate.
4. Synthetic Oxytocin (Pitocin) may produce bradycardia by causing a hyperstimulation of the uterine muscle (myometrium), resulting in hypoxia.5. Maternal Hypotension: Supine hypotension syndrome caused by pressure of the uterus and its contents on the inferior vena cava, when you lay on your back, results in decreased maternal blood pressure.6. Prolapsed Umbilical Cord or Prolonged Compression of Umbilical Cord. o Either situation may activate the fetal regulatory mechanism, causing a stimulation of the vagal center, which is part of the parasympathetic nervous system. This results in bradycardia.
What Are Causes Of Fetal Heart Rate Tachycardia?• Tachycardia: Suspicious tachycardia is defined as being between 150 and 170 whereas a pathological pattern is above 170.1. Fetal Hypoxia. Tachycardia may be an early sign of hypoxia (fetal lack of adequate oxygen).2. Medications. Medications used to prevent/stop premature labor such as terbutaline (sympathomimetic), have a stimulating effect on the fetal heart, which increases the rate.3. Prematurity. A premature baby has an immature nervous system resulting in an increased heart rate.
4. Maternal Anxiety. During periods of maternal stress and anxiety, epinephrine is released into the mother’s blood stream that crosses the placenta, resulting in an increase in fetal heart rate.5. Maternal Fever. Both the mother’s and the baby’s metabolism is increased, which results in an increased heart rate6. Fetal Infection. This may be an early sign of an intrauterine infection (a stress reaction to sepsis). Prolonged ruptured membranes may lead to maternal and fetal infection.7. Fetal Movement/Stimulation. Benign cause of fetal tachycardia.
3) Baseline FHR Variability• Fetal heart rate variability has become one of the most important indicators in the clinical assessment of fetal well-being.• Variability is indicative of a mature fetal neurologic system
What Is Fetal Heart Rate Variability?• Fetal heart rate variability is the normal irregular changes and fluctuations in the fetal heart rate that shows as an irregular heart rate seen on the tracing instead of a smooth line.• The baseline rate variability should vary by at least 10-15 beats over a period of one minute.• A decrease in variability can be noted during fetal sleep.
• Variability can be divided into the following categories: o Decreased: minimal variability (0-5 bpm). o Moderate: normal variability (6-25 bpm). o Marked: saltatory variability (>25bpm).• A normal, healthy fetal heart rate should possess average or moderate variability.
Decreased Variability May Occur in The Following Situations:1. Hypoxia and acidosis: The lack of oxygen and the build-up of acid in the fetal body depress the fetal heart and nervous system.2. All central nervous system depressant medications, including narcotics and anesthetic agents, depress the fetal nervous system. Usually, variability increases as the drug is eliminated from the baby.3. Prematurity. The fetal nervous system in a premature baby cannot effectively control the heart rate.4. Fetal sleep (as noted above).• Persistent minimal or absent variability is considered an ominous pattern, requiring immediate delivery.
4) Accelerations• The fetal heart rate will normally remain steady or accelerate during uterine contractions.• Accelerations are defined as a transient increase in heart rate of greater than 15 bpm for at least 15 seconds (the 15x15 rule).• Two accelerations in 20 minutes is considered a reactive trace.• Accelerations are a reassuring sign as they show fetal responsiveness and the integrity of the mechanisms controlling the heart.
5) Periodic or Episodic Decelerations• Periodic refers to decelerations that are associated with contractions;• Episodic refers to those not associated with contractions.• Deceleration = decrease in baseline FHR.
THREE Types of Decelerations:a) Early Decelerations:b) Late Deceleration:c) Variable Deceleration:
A - Early Decelerations:• The early deceleration begins at the onset of the contraction and ends with the end of the contraction.• Early deceleration is caused by vagal stimulation from head compression.• Early decelerations are not a sign of fetal problems .
Early Decelerations Occur Most Frequently In The Following Clinical Situations:1. During sterile vaginal examinations2. In second stage of labor during pushing3. During application of internal FHR electrode4. With cephalopelvic disproportion5. After amniotic sac has ruptured6. With vertex presentations
B - Late Deceleration:• Late decelerations are transitory decreases in heart rate caused by uteroplacental insufficiency, o a compromised blood flow to the baby that does not deliver the amount of oxygen needed to withstand the stress of labor.• The late deceleration begins after the onset of the peak or middle of the contraction and ends after the contraction.
Note:Persistent late decelerations are threatening, especially if thedecelerations are associated with loss of variability.
C - Variable Deceleration:• Variable decelerations are transitory decreases in fetal heart rate caused by umbilical cord compression.
• A variable deceleration is unrelated to contractions.• They may appear V-shaped or U-shaped.• If a woman could be monitored throughout the 9 months of her pregnancy, it would be apparent that variable decelerations occur transiently as the baby grabs the umbilical cord or the cord gets compressed between the baby and the uterine wall during fetal movement.
• Variable decelerations are not associated with poor fetal outcome.• They indicate possible compromise if they become prolonged or are persistent.
Normal/Reactive FHR Pattern1. Baseline rate 110-160 bpm2. Moderate variability (>5 bpm)3. Absence of late, or variable decelerations4. Early decelerations and accelerations may or may not be present.
Warning Patterns Suggest Decreasing Fetal Capacity To Cope With The Stress Of Labor:1. Decrease in baseline variability (<5bpm)2. Progressive tachycardia (>160bpm)3. Decrease in baseline FHR4. Intermittent late decelerations with good variability.
Ominous Patterns Suggest Possible Fetal Compromise:1. Persistent late decelerations, especially with decreasing variability.2. Variable decelerations with loss of variability.3. tachycardia, or late return to baseline4. Absence of variability5. Severe bradycardia
• If an ominous pattern appears to be present: Intrauterine Resuscitation a) Has the mother lie on her left side (remember, lying on her back invites hypotension which affects baby’s oxygen supply) or in a knee chest position. To alleviate possible cord compression. b) Reduce or stop any oxytocin she may be receiving. c) Initiate tocolytics - to decrease uterine activity and increase placental blood flow.
d) Increase IV fluid - to increase maternal blood flow volumee) Give her oxygen by mask - to promote oxygenation across the placentaf) Apply an internal monitor - to verify the accuracy of external monitor readings.g) Administer amnioinfusion - to decrease pressure on cord.• If the heart rate is not restored to normal within 30 minutes, prompt delivery is needed.• Cesarean section may then become necessary.
Effect on Management:• It has been shown that use of CTG reduces the rate of seizures in the newborn,• But there is no clear benefit in the prevention of cerebral palsy, perinatal death and other complications of labor.
• High negative predictive value : >98% of fetuses with a normal CTG will be OK.• Poor positive predictive value : 50% of fetuses with an abnormal CTG will be hypoxic but 50% will be OK.• A normal CTG is a good sign but a poor CTG does not always suggest fetal distress.