FETAL CIRCULATION AND
DR. REEM ALI
Spring Semester 2014-2015
Fetal Circulation

Placenta: delivers nutrition, O2 ,
removes waste product, protection

Umbilical cord : has two
arteries and one vein



Umbilical vein brings O2 and
nutrition to the fetus
Umbilical arteries: allow
unoxygenated blood flow from
the descending aorta back to the
placenta
Fetal lungs: filled with fluid thus
exhibit high resistance
Fetal Circulation

Foramen ovale: is anatomical opening
between the right atrium and left atrium
which closes shortly after birth.
 Ductus
arteriosus: A vessel that connects
the main pulmonary artery to the aorta.
 Ductus venosus : a channel
passing through
the liver and joining the umbilical vein with the
inferior vena cava.
Fetal Circulation

Before birth umbilical vein carries highly
oxygenated blood from the placenta to the fetal
circulation.
 Average oxygen
saturation of blood is 80% in the
umbilical vein before it mixes with
unoxygenated blood in the ductus venosus.
After mixing, the oxygen saturation is
approximately 67%.
Fetal Circulation

Due to the higher pressure of the blood in the inferior vena
cava, more blood flows from it directly into the left atrium via
the foramen ovale and a small portion of the blood seeps into
the right ventricle via the tricuspid valve.

The largest part of the blood from the right atrium flows via
the foramen ovale into the left atrium and via the mitral valve
into the left ventricle and then into the aorta

Due to the high pressure in the lungs a significantly larger
part of blood flows through the ductus arteriosus and goes
into the aorta descendens and thus directly into the large
(systemic) circulation system.
Fetal Circulation

Before birth umbilical vein carries highly
oxygenated blood from the placenta to the fetal
circulation.
 Average oxygen
saturation of blood is 80% in the
umbilical vein before it mixes with
unoxygenated blood in the ductus venosus.
After mixing, the oxygen saturation is
approximately 67%.
Changes at Birth
 First
Breath
 The
lungs are filled with air instead of fluid.
Higher oxygen levels in the blood and alveoli
allows for pulmonary vascular resistance to
decrease. This results in a greater increase in
pulmonary blood flow
Changes at Birth

Anatomical Changes
 Placenta
is removed from circulation.
 Foramen ovale and Ductus Venosus and Arteriosus are
closed.
 Higher pressure
in the left atrium due to increased
pulmonary blood flow cause the foraman ovale to close.
 Higher concentrations of oxygen in the blood, decreased
prostaglandin levels and decreased pulmonary vascular
resistance closes ductus Arteriosus . Its functionally closes
within 15 hours and structurally within a few weeks (in
mature infants)
 When the umbilical cord
is clamped, the umbilical vein
closes, systemic vascular resistance is increased and this
causes the ductus venosus to close.