The document summarizes fetal circulation and the circulatory changes that occur at birth. In the fetus, blood is shunted away from the lungs through various vessels like the ductus arteriosus and foramen ovale, since the lungs are not functional. At birth, with the first breath, pulmonary vascular resistance drops and blood flow to the lungs increases. The foramen ovale and ductus arteriosus then close over the next few days as blood pressure changes and the vessels constrict, establishing the neonatal circulation.

1. Foetal circulation and circulatory
changes at birth
Maria Idrees; PT

2. INTRODUCTION
• Fetal circulation is different from that of adults
because of the presence of placenta.
• Since fetal lungs are non functioning, placenta is
responsible for exchange of gases between fetal
blood and mother’s blood.
• So, the blood from right ventricle is diverted to
placenta.
• Development of heart is completed at 4th week
of intrauterine life and it starts beating at the rate
of 65 per minute.

3. • Along with heart, the blood vessels also
develop. Heart rate gradually increases and
reaches the maximum rate of about 140 beats
per minute just before birth.
• Fetus is connected with the mother through
placenta. Fetal blood passes to placenta
through umbilical vessels and the maternal
blood runs through uterine vessels.
• These two sets of blood vessels lie in close
proximity in the placenta through which
exchange of substances takes place between
mother’s blood and fetal blood.

5. BLOOD VESSELS IN FETUS
• As fetal lungs are non-functioning, there is no
necessity of large amount of blood to be pumped
into lungs.
• Instead, the fetal heart pumps large quantity of
blood into the placenta for exchange of
substances.
• From placenta, the umbilical veins collect the
blood, which has more oxygen and nutrients.
Umbilical vein passes through liver. Some amount
of blood is supplied to liver from umbilical vein.

6. • However, a large quantity of blood is diverted
from umbilical vein into the inferior vena cava
through ductus venosus. Liver receives blood
from portal vein also.
• In liver, the oxygenated blood mixes slightly
with deoxygenated blood and enters the right
atrium via inferior vena cava.
• From right atrium, major portion of blood is
diverted into left atrium via foramen ovale.
Foramen ovale is an opening in intra-atrial
septum.

7. • Blood from upper part of the body enters the
right atrium through superior vena cava. From
right atrium, blood enters right ventricle.
• From here, blood is pumped into pulmonary
artery. From pulmonary artery, blood enters
the systemic aorta through ductus arteriosus.
• Only a small quantity of blood is supplied to
fetal lungs. Blood from left ventricle is
pumped into aorta.
• Fifty percent of blood from aorta reaches the
placenta through umbilical arteries.

8. FETAL LUNGS
• Pulmonary vascular resistance is the resistance
offered to blood flow through pulmonary
vascular bed.
• This resistance is very high in fetus because of the
non- functioning of fetal lungs. The high
resistance in fetal lungs increases the pressure in
the blood vessels of lungs.
• Because of the high pressure, the blood is
diverted from pulmonary artery into aorta via
ductus arteriosus.

9. CHANGES IN CIRCULATION AND RESPIRATION AFTER
BIRTH – NEONATAL CIRCULATION AND RESPIRATION
1. FIRST BREATH OF THE CHILD
• When fetus is delivered and umbilical cord is cut
and tied, the lungs start functioning.
• When placental blood flow is cut off, there is
sudden hypoxia and hypercapnia.
• Now, the respiratory center is strongly
stimulated by these two factors and the
respiration starts.
• Initially, there is gasping, which is followed by
normal respiration.

10. 2. FLOW OF BLOOD TO LUNGS
• Lungs expand during the first breath of the
infant. Expansion of lungs causes immediate
reduction in the pulmonary vascular
resistance and a sudden fall in pressure in the
blood vessels of lungs. Therefore, the blood
flow from pulmonary artery to lungs
increases.

11. 3. CLOSURE OF FORAMEN OVALE
• When blood starts flowing through the
pulmonary circulation, the oxygenated blood
from the lungs returns to left atrium. It causes
increase in the left atrial pressure.
• Simultaneously, due to stoppage of blood from
placenta, pressure in inferior vena cava is
decreased. It leads to fall in right atrial pressure.
Thus, the pressure in right atrium is less and the
pressure in left atrium is already high.
• This causes the closure of foramen ovale. Within
few days after birth, the foramen ovale closes
completely and fuses with the atrial wall.

12. 4. REVERSAL OF BLOOD FLOW IN DUCTUS
ARTERIOSUS
• In fetus, since pulmonary arterial pressure is
very high, the blood passes from pulmonary
artery into aorta via ductus arteriosus.
• However, in neonatal life, since the systemic
arterial pressure is more than pulmonary
arterial pressure, the blood passes in opposite
direction in ductus arteriosus, i.e. from
systemic aorta into pulmonary aorta.
• The reversed flow in ductus arteriosus is
heard as continuous murmur in infants.

14. 5. CLOSURE OF DUCTUS VENOSUS
• Due to the contraction of smooth muscle
near junction between umbilical vein and
ductus venosus, the constriction and closure
of ductus venosus occurs.
• Later, the ductus venosus becomes fibrous
band.

15. 6. CLOSURE OF DUCTUS ARTERIOSUS
• Ductus arteriosus starts closing due to
narrowing. It closes completely after 2 days
and the adult type of circulation starts. In
some rare cases, the ductus arteriosus does
not close.
• It remains intact producing a continuous
murmur. This condition with intact ductus
arteriosus is known as patent ductus
arteriosus.