Fetal Physiology and Pathophysiology

Physiology and Pathophysiology

• This presentation covers fetal physiology and pathophysiology, including fetal circulation, fetal adaptations, baseline heart rate, variability, decelerations, and uterine contractions.
• The fetus has a higher concentration of hemoglobin and a higher affinity for oxygen than an adult, enabling it to extract more oxygen from the placenta.
• Fetal cardiac output is significantly higher than adult cardiac output.
• Fetal physiology is designed to be oversupplied with oxygen.
• The fetus is capable of accommodating significant reductions in oxygen supply through several adaptations.
• Factors influencing fetal heart rate (FHR) include the nervous system, blood pressure, blood gas levels, cord compression, hypoxia, and cerebral activity.

Fetal Circulation

• The placenta acts as a fetal lung, facilitating gas exchange between the mother and fetus.
• Deoxygenated blood flows to the placenta via umbilical arteries.
• The placenta facilitates gas exchange.
• Oxygenated blood returns to the fetus via the umbilical vein.
• Free gas exchange depends on normal maternal blood flow through the placental bed and normal blood flow through the placenta.

Fetal Adaptations

• The fetus can adjust its circulation to prioritize critical organs (brain, heart, and adrenal glands) when faced with decreased oxygen supply.
• The fetus can compensate for reduced oxygen supply by increasing oxygen extraction and centralizing blood flow.
• Oxygen is crucial in aerobic metabolism of glucose to produce energy.
• Damage to the heart or brain occurs with profound hypoxia, severe oxygen restriction.
• Reduced maternal blood supply during labour is compensated for by fetal heart adaptation.

Baseline Heart Rate

• Baseline heart rate is a proxy measure of cardiac output, reflecting the work of the heart.
• Baseline heart rate is influenced by circulatory function for oxygen delivery and carbon dioxide removal.
• Increased baseline rate indicates increased circulation.

Variability

• Variability refers to short-term fluctuations in baseline heart rate.
• Normal heart rate variability indicates good neurological function and fetal wellbeing.
• Reduced variability may be a sign of fetal distress, such as from hypoxaemia or inadequate oxygen supply.
• Reduced variability can result from hypoxaemia and chronic hypoxaemia.

Decelerations

• Decelerations are transient falls in fetal heart rate.
• They can be caused by various factors, such as head compression, cord compression, and reduced oxygen supply.
• Decelerations are crucial for evaluating fetal physiological state, often associated with reduced oxygen delivery.
• Early decelerations, variable decelerations, and late decelerations are different types of decelerations.
• Decelerations are 'lost heart beats'.

Uterine Contractions

• Uterine contractions are essential for labour progression.
• They temporarily interrupt blood flow across the placenta, reducing oxygen supply to the fetus.
• Carbon dioxide elimination from the fetus is also temporarily reduced.
• Fetal recovery of oxygen and carbon dioxide exchange is essential between contractions, particularly during strong contractions.

Sinusoidal Patterns

• A sinusoidal pattern in fetal heart rate implies severe fetal compromise, possibly from chronic hypoxaemia and/or hypoxia.
• This pattern indicates significant, ongoing oxygen deprivation.
• The inability of the fetus’ central nervous system to maintain adequate heart rate implies poor fetal well-being.

Summary

• The presented material highlights fetal physiology, adapting to labour.
• Normal physiology, adaptation, baseline rate, variability, decelerations, and abnormal patterns are critical points.