Related Experiment Video
Updated: Feb 20, 2026

Murine Fetal Echocardiography
Published on: February 15, 2013
Correlation Between the Thymic-Thoracic Ratio and Cardiac Axis in Healthy Fetuses
Objectives:
The aim of this study was to assess the correlation between the thymic-thoracic ratio and cardiac axis in healthy fetuses.
Methods:
The fetal thymic-thoracic ratio and cardiac axis were measured in 220 healthy fetuses. The normal ranges of the fetal thymic-thoracic ratio and cardiac axis for each gestational week were established. The Pearson correlation coefficient was calculated to analyze the relationship between the thymic-thoracic ratio and cardiac axis.
Results:
The mean fetal thymic-thoracic ratio increased slightly throughout the pregnancy, from 0.33 at 17 weeks' gestation to 0.37 at 37 weeks. No statistically significant correlation was found between the thymic-thoracic ratio and cardiac axis in healthy fetuses.
Conclusions:
In healthy fetuses, the thymus occupies an increasingly larger portion of the upper mediastinum when the pregnancy advances. The cardiac axis is not affected by the thymic-thoracic ratio in healthy fetuses.
Related Concept Videos
Thoracic Aorta
Fetal Circulation
Two umbilical arteries transport blood from the fetus to the placenta. At the placenta, the blood absorbs oxygen and nutrients while simultaneously eliminating waste products. This oxygen-enriched and nutrient-rich blood then returns to the fetus through one...
Correlation between ECG and Cardiac Cycle
A cardiac action potential originates in the SA node and spreads throughout the atria and the AV node in approximately 0.03 seconds. This results in the P wave in an ECG and triggers atrial contraction. The action potential is then briefly slowed at the AV node, allowing the atria to contract and fill the ventricles with blood before...
Development of the Heart
As the embryo undergoes lateral folding, these paired tubes approach each other, merging into a single primitive heart...
Pressure Relationships in Thoracic Cavity
Breathing Mechanisms
Both intra-alveolar and intrapleural pressures rely on specific lung properties. The ability to breathe—allowing air to enter the lungs...

