From the Research
Fetal circulation is a complex and highly specialized system that ensures the developing fetus receives oxygenated blood and nutrients from the placenta while bypassing the non-functioning lungs, with the most recent and highest quality study 1 providing valuable insights into the hemodynamic changes in fetal circulation. The key structures in fetal circulation include the umbilical cord (containing two arteries and one vein), the ductus venosus, foramen ovale, and ductus arteriosus.
- Oxygenated blood from the placenta enters the fetus through the umbilical vein and passes through the ductus venosus, bypassing the liver, to enter the inferior vena cava.
- Most of this blood is then shunted through the foramen ovale (an opening between the right and left atria) directly to the left side of the heart, avoiding the pulmonary circulation.
- Blood that does enter the right ventricle is largely diverted away from the lungs through the ductus arteriosus, which connects the pulmonary artery to the aorta.
- Deoxygenated blood returns to the placenta via the umbilical arteries. After birth, these fetal structures close as the newborn begins to breathe independently.
- The foramen ovale closes to become the fossa ovalis,
- the ductus arteriosus becomes the ligamentum arteriosum, and
- the ductus venosus becomes the ligamentum venosum. This transition from fetal to neonatal circulation is crucial for normal cardiovascular function after birth, as highlighted in a study on the physiology of fetal and transitional circulation 2. The use of colour Doppler ultrasound has been shown to be effective in monitoring the hemodynamic parameters of fetal uterine artery, umbilical artery, and middle cerebral artery during pregnancy, and can serve as a reference for determining the intrauterine state of the fetuses and predicting bad pregnancy outcomes 1. In addition, low-dose aspirin has been studied for its effects on uterine and fetal blood flow during pregnancy, with one study finding no significant difference in uterine, umbilical, aortic, middle cerebral, and ductus arteriosus blood flow between the aspirin group and controls 3.