Fetal cardiac position refers to the position of the heart within the chest regardless of the fetal cardiac axis or chamber orientation.
Levocardia is a term to describe a heart that is in the normal side of the thoracic cavity (left side) with apex pointing leftward.
As opposed to levocardia, dextrocardia is a term to describe a heart that is located in the right side of the thoracic cavity with apex pointing rightward. In dextroposition, which is considered a form of dextrocardia, while the heart is located in the right thoracic cavity, the apex of the heart points leftward (or medially). Dextroposition usually occurs secondary to extracardiac pathologies, such as agenesis of the right lung, space-occupying lesion in the left thoracic cavity or left lung mass. The term dextroposition describes temporary location of the heart within the right chest and that this condition should improve or resolve once the underlying pathology is treated.
Mesocardia refers to a central position of the heart within the chest.
Technique to establish fetal position in the uterus:
- Locate the fetal head within the uterus and determine the fetal presenting part (cephalic (head down) or breech (bottom down))
- Determine the fetal lie witin the uterus by obtaining a sagittal view of the fetal spine. In relation to the maternal spine, if fetal spine is i) parallel (lingitudinal fetal lie), ii) perpendicular (transverse fetal lie), iii) oblique (oblique fetal lie)
- Obtain a transverse view of the fetal abdomen by rotating transducer 90 degrees (clock-wise) from the sagittal view of the lower thoracic spine.
- Determine the location of the fetal left side within the uterus (anterior (closer to the transducer), posterior (closer to the maternal spine), right lateral (facing mother's right side), and left lateral (facing mother left side). The fetal stomach (in the left side of the abdomen), decsending aorta (posterior and to the left), and inferior vena cava (anterior and to the right) can be profiled on this view.
- By moving the transducer toward the fetal chest, heart is seen in the left side of the chest with apex pointing leftward and the four-chamber view of the fetal heart is obtained.