1
Q
What does the abbreviation MVU stand for in fetal monitoring?
A
Montevideo Units
2
Q
In obstetric monitoring, what is a TOCO?
A
Tocodynamometer
3
Q
What device is used as an internal monitor to measure both contraction frequency and strength?
A
Intrauterine Pressure Catheter (IUPC)
4
Q
What does the abbreviation FSE stand for?
A
Fetal Scalp Electrode
5
Q
What does the abbreviation CPD stand for in the context of labor?
A
Cephalopelvic Disproportion
6
Q
What does the abbreviation BPP stand for regarding fetal assessment?
A
Biophysical Profile
7
Q
What is the primary organ of gas, nutrient, and waste exchange for the fetus?
A
The placenta
8
Q
Contrast the structural arrangement of fetal circulation with adult circulation.
A
Fetal circulation is parallel, whereas adult circulation is in series.
9
Q
Name the three anatomic communications (shunts) unique to fetal circulation.
A
Ductus Venosus, Foramen Ovale, and Ductus Arteriosus.
10
Q
Describe the state of Pulmonary Vascular Resistance (PVR) in the fetus.
A
PVR is high because the lungs are collapsed and fluid-filled; very little pulmonary circulation
11
Q
Describe the state of Systemic Vascular Resistance (SVR) in the fetus.
A
SVR is low due to the low resistance vascular bed of the placenta.
12
Q
How does the oxygen affinity of Fetal Hemoglobin (HbF) compare to Adult Hemoglobin (HbA)?
A
HbF has a higher affinity for oxygen than HbA
13
Q
Which vessel in the umbilical cord carries oxygenated blood from the placenta to the fetus?
A
Umbilical Vein
14
Q
How many umbilical arteries are typically found in the umbilical cord?
A
Two
15
Q
What type of blood is carried by the umbilical arteries?
A
Deoxygenated (oxygen-poor) blood
16
Q
What is the function of the Ductus Venosus (DV)?
A
It allows oxygenated blood to bypass the immature portal circulation and enter the inferior vena cava directly.
17
Q
How does the percentage of blood directed to the fetal liver change during gestation?
A
It increases with gestational age.
18
Q
What anatomic opening directs oxygenated blood from the Right Atrium to the Left Atrium?
A
Foramen Ovale (FO)
19
Q
Why does a right-to-left shunt occur through the Foramen Ovale in the fetus?
A
High fetal PVR creates a pressure gradient where Right Atrial pressure is greater than Left Atrial pressure.
20
Q
What is the function of the Ductus Arteriosus (DA)?
A
It connects the Pulmonary Artery to the Descending Aorta to divert blood away from the lungs.
21
Q
Blood exiting the Left Ventricle into the Ascending Aorta primarily supplies which fetal areas?
A
Coronary and cerebral circulation (upper body).
22
Q
What percentage of blood from the fetal Right Ventricle actually passes through pulmonary circulation?
A
Approximately 10%
23
Q
Which pressure relationship is greater in fetal circulation: PVR or SVR?
A
PVR > SVR
24
Q
What is the path of fetal blood flow starting with the RA?
A
RA - FO - LA - LV - AA - systemic circulation
25
How soon after delivery do neonatal respiratory efforts typically begin?
30-90 seconds
26
What effect does air entering the lungs have on neonatal PVR?
It causes PVR to decrease
- intrathoracic pressure dec, air enters lungs - inc PaO2 and dec PaCO2, inc pH and alveolar O2 tension, dec PVR
27
What event triggers the closure of the Ductus Arteriosus?
constricts and closes due to inc oxygen levels
28
What immediate post-delivery action triggers an increase in neonatal SVR?
Clamping of the umbilical cord - inc SVR, inc LA pressure, dec R-L shunt
29
What specific pressure change causes the Foramen Ovale to close after birth?
Left atrial pressure exceeds right atrial pressure.
30
What event triggers the closure of the Ductus Venosus?
Clamping of the umbilical cord - inc IVC pressure
31
Identify four factors that can impede the successful transition from fetal to neonatal circulation.
Hypoxia, acidosis, hypovolemia, and hypothermia - causes PVR to remain high
32
Maternal use of which class of medications can cause premature constriction of the Ductus Arteriosus?
NSAIDs
33
What are the 5 major causes of PPHN?
- premature constriction of the ductus arteriosus
- mec aspiration
- sepsis
- perinantal asphyxia
- hypothermia
34
What do fetal baroreceptors detect?
Changes in blood pressure - aortic arch, carotid arteries
35
What three variables do fetal chemoreceptors monitor?
Hypoxia, hypercapnia, acidosis
36
During initial hypoxia (e.g., cord compression), what is the primary fetal heart rate response?
Bradycardia due to increased vagal activity.
37
38
What is the fetal heart rate response to prolonged hypoxia (more than a few minutes)?
Tachycardia due to sympathetic nervous system activation and catecholamine secretion.
39
What is the long-term risk of prolonged fetal hypoxia?
- Fetal growth restriciton
- Impaired brain and kidney function
- Apoptosis of cardiomyocytes
- fetal demise
40
Which uterine monitor can only determine contraction frequency, not strength?
External monitor (Tocodynamometer)
41
Why is placental reserve critical during uterine contractions?
Blood flow decreases during contractions, so the fetus must rely on stored oxygen until flow resumes.
42
What are the placental causes of impaired fetal oxygenation?
Abruption, infarction, too small, inc placental resistance (not likely reversible)
43
What are the uterine causes of impaired fetal oxygenation?
Tachysystole and tetanic contraction
44
What are the maternal causes of impaired fetal oxygenation?
Hypotension and hypoxia
45
How is contraction frequency quantified?
Counted over 10 minute period, averaged over 30 minutes, from beginning of one to the beginning of the next
=/< 5 contractions in 10 min is normal
46
Define Tachysystole in terms of contraction frequency.
More than 5 contractions in 10 minutes, averaged over a 30-minute period.
47
List two medications used to relax the uterus in the event of tachysystole.
Nitroglycerine (SL or IV) and Terbutaline.
48
What is the defined range for a normal Fetal Heart Rate (FHR) baseline?
110-160 bpm
49
Fetal tachycardia is defined as a baseline heart rate greater than _____.
160 bpm
50
Fetal bradycardia is defined as a baseline heart rate less than _____.
110 bpm
51
What is considered the single most important indicator of an adequately oxygenated fetus?
Fetal Heart Rate (FHR) variability
52
Define 'Absent' FHR variability.
The amplitude range is undetectable.
53
Define 'Minimal' FHR variability.
The amplitude range is less than or equal to 5 bpm.
54
What is the amplitude range for 'Moderate' FHR variability?
6-25 bpm
55
Define 'Marked' FHR variability.
The amplitude range is greater than 25 bpm.
56
List the 9 substances that can cause minimal or absent FHR variability.
Magnesium sulfate, systemic opioids, and benzodiazepines.
57
List the non-substance causes of minimal/absent variability
- Fetal sleep cycles
- Prematurity
- Arrhythmias
- Fetal tachycardia
- Pre-existing neurological abnormality
- Congenital anomalies
- Severe hypoxemia
58
How is FHR variability quantified?
Amplitude of peak-to-trough bpm
59
What are the three categories of FHR decelerations based on pattern?
Early, Variable, and Late (Pattern)
60
What is the physiological cause of Early Decelerations?
Fetal head compression leading to vagal stimulation d/t altered CBF
61
How are early decelerations seen on a strip?
- Symmetric gradual decrease in FHR with return to baseline
- Onset of decel to nadir (lowest point) of FHR = / > 30 seconds
- Nadir of FHR deceleration at peak of contraction
62
What is the physiological cause of Variable Decelerations occuring in early labor?
Umbilical cord compression; can also be frequent variable decels in later stage
63
Describe how variable decelerations appear on a strip
- Onset, depth, duration vary w/contractions
- Typically jagged & irregular. U, V, or W shape
- *Abrupt* decrease in FHR & abrupt return to baseline
- Onset of decel to beginning of FHR nadir < 30 secs
- FHR decreases 15 bpm or more
- Lasts 15 seconds or longer, < 2-minute duration
64
Variable decelerations are caused by
Transient hypoxemia
65
What are other causes of variable decelerations?
- True knot
- Nuchal cord
- Short cord
- Rapid fetal descent
- Oligohydramnios (low amniotic fluid)
- **2nd stage of labor: fetal head compression** (Dural stimulation → increased vagal discharge)
66
What are the causes of Late Decelerations?
- Hypoxemia: Continued hypoxia → lactic acidosis
- This would be seen as a late decel + fetal tachycardia with minimal variability
- Myocardial decompensation & failure
- Chorioamnionitis
- Post-term gestation
- Uterine hyperactivity
- Maternal hypotension / hypertensive disorders / cardiac disease
- Maternal smoking
- Maternal anemia
- Placental abruption / previa
67
What kind of decels are ominous?
Late decels with decreased / absent FHR variability
68
A deceleration is defined as 'prolonged' if it lasts between _____ and _____ minutes.
2 minutes; 10 minutes
69
How are severe decelerations defined?
- FHR < 70 bpm
- Decrease in FHR > 60 bpm from baseline
- Contraction duration > 60 seconds
- Decreased umbilical blood flow
- Impaired fetal cardiac output
70
What aer the causes of prolonged decelerations?
- Umbilical cord compression
- Prolonged maternal hypotension/hypoxia
- Tetanic uterine contractions
- Prolonged head compression in 2nd stage of labor
71
What does a Sinusoidal FHR pattern typically indicate?
Fetal anemia, Rh disease, or severe hypoxia
72
What characterizes a Category I FHR tracing?
Baseline 110-160 bpm, moderate variability, and no late or variable decelerations.
73
How is a sinusoidal pattern recognized on a strip?
- Smooth, wave-like, undulating pattern
- Cycle frequency of 3-5 cycles per minute
- Amplitude range of 5-15 bpm
- Persists > 20 minutes
- Requires obstetrical intervention
74
Describe the 6 steps of FHR interpretation (ACOG)
1. Assess Uterine Contractions (Bottom Strip)
- Normal: ≤ 5 contractions in 10 minutes (avg over 30 min)
- Tachysystole: > 5 contractions in 10 minutes
- Note presence or absence of FHR decelerations
2. Assess FHR Baseline (Top Strip)
- Look at baseline over a 10-minute window (requires at least 2 minutes of identifiable baseline)
- Normal: 110–160 bpm
- Tachycardia: > 160 bpm
- Bradycardia: < 110 bpm
3. Evaluate Baseline Variability
- Absent: Undetectable
- Minimal: ≤ 5 bpm
- Moderate (normal): 6–25 bpm
- Marked: > 25 bpm
4. Evaluate Decelerations
5. Assign a Category
6. Remember that context matters!
75
What criteria define a Category I FHR tracing?
Predictive of normal fetal acid-base status:
- Baseline FHR 110 - 160 bpm
- Moderate baseline variability
- No late or variable decelerations
- Early decelerations present/absent
- Accelerations present/absent
76
What criteria define a Category II FHR tracing?
Indeterminate
- Fetal tachycardia
- Absence of induced accelerations after fetal stimulation
- Prolonged decelerations > 2 mins < 10 mins
- Recurrent late decels w/ moderate variability
- *Not predictive of abnormal fetal acid-base status*
77
What criteria define a Category III FHR tracing?
Abnormal fetal acid-base status
- Absent variability PLUS one of the following: recurrent late decels, recurrent variable decels, or bradycardia (OR a sinusoidal pattern).
78
How is a category III FHR tracing category managed?
- Maternal position change
- Discontinue labor augmentation
- Treatment of tachysystole
- Surgical delivery
79
What is the primary purpose of the APGAR scoring system?
To determine which neonates require resuscitation.
80
Name the five components of the APGAR score.
Heart rate, respiratory effort, muscle tone, reflex irritability, and color.
81
An APGAR score of _____ indicates a need for immediate resuscitation.
0-3
82
What APGAR score indicated moderate impairement?
4-7
83
What APGAR score is considered normal?
8-10
84
At what time intervals is the APGAR score typically performed after birth?
1 minute and 5 minutes, given a score of 0, 1, or 2
85
Risk of mortality is _________ proportional to 1 min APGAR score
inversely
86
What uterine condition is characterized by an abnormally long contraction with no period of relaxation?
Tetanic contraction
87
How does maternal hypotension affect fetal oxygenation?
It reduces uterine blood flow (UBF), potentially leading to fetal hypoxemia.
88
What is the effect of adenosine accumulation in the hypoxic fetus?
It causes vasodilation of cerebral vessels to maintain oxygen delivery to the brain.
89
In the fetus, where does the highest oxygenated blood go after passing through the Foramen Ovale?
To the heart (coronaries) and brain.
90
What fetal monitoring finding is considered 'Ominous'?
Late decelerations combined with decreased or absent FHR variability.
91
What does an FHR baseline change require in terms of duration?
The rate change must last at least 10 minutes.
92
Which specific fetal shunt allows blood to bypass the liver?
Ductus Venosus
93
Which fetal shunt moves blood from the Pulmonary Artery to the Aorta?
Ductus Arteriosus
94
Explain why fetal circulation is described as 'parallel'.
Both the right and left sides of the heart provide systemic blood flow simultaneously.
95
How does the fetus compensate for low arterial oxygen tension (PaO2)?
By using HbF with high oxygen affinity and maintaining a high cardiac output.
96
What are the fetal and maternal causes of fetal tachycardia?
- Fetal: chorio, sepsis, acute fetal hypoxia (more than few min), fetal heart failure, and anemia
- Maternal: hyperthyroidism, fever, epinephrine/ephedrine, beta-2 adrenergic agonists (ritodrine/terbutaline)
97
What are the causes of fetal bradycardia?
- Hypoxemia (Initial response, umbilical cord compression, fetal head compression)
- Hypothermia
- Maternal hypotension – can be caused by us!
- Maternal hypoglycemia
- Congenital heart block
Advanced Principles A
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