Fetal Circulation and Heart Rate Basics

Questions and Answers

Ductus venosus connects to ?

Umb. vein to IVC

Foramen ovale connects to ?

R. atrium to L. atrium

Ductus arteriosus connects to ?

Pulm. artery to aorta

What is the normal heart rate range for a fetus?

110 to 160 BPM Signup and view all the answers

What is the average baseline rate at 15 weeks gestation?

160 BPM Signup and view all the answers

What is the average heart rate in a fetus with heart block?

60 BPM Signup and view all the answers

What are sympathetic effects on heart rate?

Increased heart rate and constricted blood vessels Signup and view all the answers

At what gestational age is the autonomic nervous system fully developed?

~ 32 weeks Signup and view all the answers

What is the primary indicator of fetal oxygenation?

Presence or absence of variability Signup and view all the answers

Where are the chemoreceptors located?

Aortic arch Signup and view all the answers

What do chemoreceptors respond to?

Changes in O2 and CO2 Signup and view all the answers

Where are the baroreceptors located?

Aortic arch and carotid bodies Signup and view all the answers

When does maximal reactivity occur?

Late at night Signup and view all the answers

What is the maximum duration of fetal nonreactivity?

80 minutes Signup and view all the answers

What does sensitivity indicate?

Probability of detecting a true positive Signup and view all the answers

What does specificity indicate?

Probability that a true negative will be detected Signup and view all the answers

What is a false positive?

Erroneously positive when reality is negative Signup and view all the answers

What is a false negative?

Erroneously negative when reality is positive Signup and view all the answers

What constitutes a non-stress test (NST)?

Two 15x15 accels in 20 min Signup and view all the answers

What percentage of false positive CSTs is typical?

~ 30% Signup and view all the answers

What are the components of the Biophysical Profile (BPP)?

Fetal breathing movements, gross body movements, fetal tone, reactive fetal heart rate, qualitative amniotic fluid volume Signup and view all the answers

What is a BPP score of 10 indicative of?

Normal Signup and view all the answers

What does a BPP score of 8 suggest?

Nl infant, low risk of chronic asphyxia Signup and view all the answers

What does a BPP score of 6 indicate?

Borderline result - repeat in 24 hours Signup and view all the answers

What does a BPP score of 4 suggest?

Suspect chronic asphyxia Signup and view all the answers

What does a BPP score of 0-2 indicate?

Strongly suspect chronic asphyxia Signup and view all the answers

What is an early manifestation of fetal acidosis?

Non-reactive NST and loss of fetal breathing movements Signup and view all the answers

How does maternal glucose level affect fetal breathing movements (FBM)?

FBM increases with rising maternal glucose, FBM decreases with maternal hypoglycemia Signup and view all the answers

How does maternal smoking affect fetal breathing movements?

FBM decreases with smoking Signup and view all the answers

What is the effect of corticosteroids on fetal breathing movements?

Corticosteroids may decrease FBM Signup and view all the answers

What is the maternal PAO2 at sea level?

~ 105 mmHg Signup and view all the answers

How do cardiac output and systemic vascular resistance (SVR) change in pre-eclampsia?

CO and SVR increased in pre-E Signup and view all the answers

In what percentage of uterine rupture cases do prolonged decelerations occur?

71% Signup and view all the answers

What is the significant duration between the onset of HFR deceleration and delivery that affects neonatal morbidity?

18 minutes Signup and view all the answers

What is the normal arterial pH for healthy vaginal deliveries?

7.28 +/- 0.05 Signup and view all the answers

What is the normal arterial pO2 for healthy vaginal deliveries?

18.0 +/- 6.2 Signup and view all the answers

What is the normal arterial pCO2 for healthy vaginal deliveries?

49.2 +/- 8.4 Signup and view all the answers

What is the normal base deficit for healthy vaginal deliveries?

Less than 12 Signup and view all the answers

What pH level indicates acidosis?

7.2 (7.1) Signup and view all the answers

What is tachysystole?

<blockquote> 5 contractions in 10 min </blockquote> Signup and view all the answers

What is the definition of baseline in fetal heart rate monitoring?

Mean FHR rounded to increments of 5 BPM during a 10-minute period, excluding certain changes Signup and view all the answers

What does a sinusoidal pattern indicate?

Fetal anemia Signup and view all the answers

What percentage of infants with complete heart block have associated congenital cardiac malformations?

50% Signup and view all the answers

What is the mortality rate for newborns with complete heart block?

25% Signup and view all the answers

A newborn with complete heart block in the absence of congenital heart disease frequently has what condition?

Lupus erythematosus Signup and view all the answers

What is the definition of baseline variability?

Fluctuations in baseline FHR >2 cycles per minute Signup and view all the answers

What is minimal baseline variability?

<blockquote> undetectable but 25 bpm </blockquote> Signup and view all the answers

Performing fetal stimulation is appropriate during decelerations or bradycardia.

False Signup and view all the answers

What is an early deceleration?

Visually apparent gradual decrease in FHR below baseline during contractions Signup and view all the answers

What is the physiology behind early decelerations?

Fetal head compression (vagal reflex) Signup and view all the answers

Study Notes

Fetal Circulation Connections

Ductus venosus connects umbilical vein to inferior vena cava (IVC).
Foramen ovale connects right atrium to left atrium.
Ductus arteriosus connects pulmonary artery to aorta.

Fetal Heart Rate

Normal fetal heart rate ranges between 110 to 160 beats per minute (BPM).
Average baseline rate at 15 weeks gestation is 160 BPM.
In a fetus with heart block, the average rate is 60 BPM.

Autonomic Nervous System and Fetal Response

Autonomic nervous system fully develops around 32 weeks of gestation.
Sympathetic nervous system increases heart rate and constricts peripheral blood vessels while dilating vital organs for better blood flow.

Indicators of Fetal Oxygenation

Primary indicator of fetal oxygenation is the presence or absence of variability in heart rate.
Location of chemoreceptors is in the aortic arch, responding to changes in oxygen (O2) and carbon dioxide (CO2) levels.
Location of baroreceptors includes the aortic arch and carotid bodies.

Fetal Heart Rate Reactivity

Maximal reactivity of fetal heart rate typically occurs late at night.
Fetal nonreactivity may last for a maximum of 80 minutes.

Diagnostic Test Parameters

Non-Stress Test (NST) requires two accelerations of 15 beats per minute lasting at least 15 seconds within a 20-minute period (may be extended to 40 minutes).
Approximately 30% of contraction stress tests (CSTs) yield false positives.

Biophysical Profile (BPP) Components and Scoring

BPP evaluates: fetal breathing movements, gross body movements, fetal tone, reactive fetal heart rate, and qualitative amniotic fluid volume.
BPP score of 10 indicates normal conditions.
BPP score of 8 suggests a normal infant with low risk of chronic asphyxia.
Scores of 6 indicate a borderline result requiring re-evaluation within 24 hours.
A score of 4 raises suspicion for chronic asphyxia, while a score of 0-2 strongly suspects it.

Fetal Acidosis and Influencing Factors

Early signs of fetal acidosis include non-reactive NST and loss of fetal breathing movements (FBM).
Fetal breathing movements increase with rising maternal glucose and decrease with maternal hypoglycemia.
Maternal smoking decreases fetal breathing movements while corticosteroids may also lead to decreased FBM.

Maternal and Fetal Physiological Metrics

Maternal arterial oxygen pressure (PAO2) at sea level approximates 105 mmHg.
In pre-eclampsia, cardiac output (CO) and systemic vascular resistance (SVR) increase.
Prolonged late decelerations occur in 71% of cases of uterine rupture.

Neonatal Health Indicators

Significant neonatal morbidity occurs when 18 minutes or longer elapse from the onset of heart rate deceleration until delivery.
Normal arterial pH for healthy vaginal deliveries is 7.28 ± 0.05.
Normal ranges for arterial pO2 and pCO2 are 18.0 ± 6.2 and 49.2 ± 8.4 respectively, with a normal base deficit being less than 12.
Acidosis is indicated when pH falls to 7.2 (or lower).

Heart Rate Dynamics

Tachysystole is defined as more than five contractions within ten minutes.
Baseline fetal heart rate (FHR) is the average rate rounded to the nearest 5 BPM over a 10-minute period, excluding periodic changes.
A sinusoidal pattern in FHR typically indicates fetal anemia.

Congenital Heart Block Statistics

Approximately 50% of infants with complete heart block have associated congenital cardiac malformations.
Mortality rate for newborns with complete heart block is around 25%.
Newborns with complete heart block, without underlying congenital heart disease, frequently exhibit neonatal lupus erythematosus.

Variability in Fetal Heart Rate

Baseline variability consists of fluctuations in the FHR exceeding two cycles per minute, characterized by irregular amplitude and frequency.
Minimal variability is defined as undetectable but can be greater than 25 BPM.

Test Performance Guidelines

Fetal stimulation during decelerations or bradycardia is not appropriate; stimulation should occur when the FHR is at baseline.

Deceleration Characteristics

Early decelerations are gradual decreases in FHR below baseline, with the nadir occurring at the peak of a contraction and taking at least 30 seconds from onset to nadir.
Physiology of early decelerations is attributed to fetal head compression triggering a vagal reflex, often observed between 4-6 cm dilation.

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Description

Test your knowledge on fetal circulation connections and heart rate norms. This quiz covers key concepts including the autonomic nervous system's role and indicators of fetal oxygenation. Perfect for students studying fetal development and physiology.