FETAL CIRCULATION

BEFORE
AND
AFTR BIRTH

Dr. Zahid Kaimkhani

FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

"Nature is neither lazy nor devoid of foresight. Having given

the matter thought, she knows in advance that the lung of the
fetus does not require the same arrangements of a perfected
lung. She has therefore anastomosed the pulmonary artery
with the aorta, and the left and right atria. . . .“ -Galen, 2nd
Century (129-200)

The fetal CVS is designed to:

• Serve prenatal needs
• Permit modification at birth ( to establish
the neonatal circulatory pattern
 Good respiration
in the newborn infant
is dependent upon
normal circulatory
changes
at birth.
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

FETAL CIRCULATION
Most important vascular structures in
transitional circulation are:
§ Ductus venosus
§ Oval foramen
§ Ductus arteriosus

35%
65%
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

§ Blood reaches & leaves the fetus

through the umbilical cord.

§ The umbilical cord contains

• Two arteries and
• One vein.
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

§ Highly oxygenated blood passes from

the placenta through the umbilical Ductus Venosus

vein.

§ Half of this blood reaches the IVC

through the ductus venosus.

§ The other Half passes to liver

sinusoids then to the IVC.
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

§ Blood of the IVC reaches the right

atrium, then left atrium through the
Foramen Ovale.

§ Then to the left ventricle to the

ascending aorta, and the aortic
arch to supply head & neck brain,
cardiac muscle and upper limbs.
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

Ductus Arteriosus

Small amount of highly oxygenated blood

in right atrium mixes with venous blood of
the SVC passes to RIGHT VENTRICLE .

Then to the pulmonary artery

Then thru Ductus Arteriosus (between
the Pulmonary trunk & Proximal part of
the descending aorta), to the fetal body.
And then back to placenta via the umbilical
arteries.
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

Fetal circulation before birth

Arrows, direction of blood flow.

NOTE: Where oxygenated blood mixes

with deoxygenated blood:
I. In the liver,
II. In the inferior vena cava,
III. In the right atrium
IV.In the left atrium, and
V. at the entrance of the ductus
arteriosus into the descending
aorta.
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTER BIRTH
BEFORE BIRTH
Blood from the placenta (80% saturated with O2)

Thru umbilical vein

return to fetus
At Liver
• Most of the blood enter THE DUCTUS VENOSUS [DV] ( bypass the liver) and
flows directly to IVC (half in KLM}
• A smaller amount enter the liver sinusoids and MIXES with blood from
portal circulation (GIT)

Is there a sphincter mechanism in DV?

• YES , MORE physiological then anatomical
• Close to the entrance of the umbilical vein
• Regulates flow of umbilical blood thru the liver sinusoids
• Closes during uterine contraction (venous return too high)
• To prevent the overloading of the heart

At inferior vena cava

• a short course
• Mixing of placental blood with deoxygenated blood from LL, abd & pelvis
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

Right Atrium (RA)

• Guided towards the foramen oval ( by the valve of
IVC)
• Most of the blood passes directly to the left atrium
• Small amount fails and remain in the RA ( bcz of the
crista dividens --- lower edge of septum secundum)
• Another mixing –with deoxygenated blood thru SVC

Left Atrium (RA)

• Another mixing –with small amount desaturated blood
returning from LUNGs

• Left ventricle
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

• Ascending aorta

• Organ supplied with Well-Oxygenated blood

• Heart and brain (H&N &UL)–coronary and carotid arteries are
the first branches of the AA
• Another shunt and Mixing –Ductus arteriosus
• RA ( desaturated blood thru SVC) to RV –to pulmonary trunk
thru
• High resistance in pulmonary vessels
• Causes most of the blood passes directly to Descending Aorta
via Ductus arteriosus
• Last mixing with blood from proximal aorta
• Finally blood flows toward the fetal body and placenta thru
two umbilical arteries (o2 saturation is approx. 58%)
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

CIRCULATORY CHANGES
AFTR BIRTH
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

Ligation of the umbilical cord

Sudden fall of blood pressure in the IVC and the
right Atrium.
The wall of the ductus venosus constricts.

Aeration of the lungs at birth

1- Marked increase in the pulmonary blood flow.
2- Dramatic fall in pulmonary vascular resistance.
3- Thinning in the wall of the pulmonary arteries.
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

1. Closure of foramen ovale:

a. Physiological closure
b. Anatomical closure.

2- Constriction of ductus arteriosus:

By the end of the first 24 hours 20% of the lumen of
the ductus is closed.
By the end of 48 hours 82% is closed.
By 96 hours 100% of the duct is closed.
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

BRADYKININ:
• released from fetal lungs during their initial inflation.

• has a contractile effect on smooth muscles of the ductus arteriosus.

• action appears to be dependent on the high Oxygen saturation

of the aortic blood.

When oxygen tension reaches 50 mmHg in the ductus arteriosus it causes

constriction of its smooth muscles.

During intrauterine fetal life the patency of ductus arteriosus (before birth)
is controlled by the low contents of oxygen in the blood passing through it.

So hypoxia and other ill-defined factors keep the ductus arteriosus patent.
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

Functional Anatomical Remnant

Closure Closure

Umbilical arteries Few minutes after birth 2-3 month Medial umbilical ligament( distal part)
Superior Vesical arteries (proximal part)
Umbilical veins Shortly after umbilical Ligamentum teres hepatis
arteries
Ductus Venosus Shortly after umbilical Ligamentum venosum
arteries
Foramen Ovale First few breaths / few 3rd month Fossa ovalis
days (KLM) In 20% Probe patent foramen ovale
1 year
(langman)
Ductus Arteriosus Almost immediately 1-3 month Ligamentum arteriosus
after birth
Anomaly
Patent Ductus Common anomaly Maternal rubella infection in early pregnancy
Arteriosus [PDA] 2-3 time more in females Premature and born at high altitude
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

Closure of the umbilical arteries,

• Accomplished by contraction of the smooth musculature in their walls,
• is probably caused by thermal and mechanical stimuli and a change in
oxygen tension.

• Functionally, the arteries close a few minutes after birth, although the actual
obliteration of the lumen by fibrous proliferation may take 2 to 3 months.

• Distal parts of the umbilical arteries form the medial umbilical ligaments, and
• the proximal portions remain open as the superior vesical arteries.

Closure of the umbilical vein and ductus venosus

• occurs shortly after that of the umbilical arteries. (ALLOWS the blood from
the placenta may enter the newborn for some time after birth).

• After obliteration, the umbilical vein forms the ligamentum teres hepatis in
the lower margin of the falciform ligament.

• The ductus venosus, which courses from the ligamentum teres to the inferior
vena cava, is also obliterated and forms the ligamentum venosum.
 .
FETAL CIRCULATION AND CIRCULATORY CHANGES AFTR BIRTH

Closure of the ductus arteriosus

• by contraction of its muscular wall occurs almost immediately after birth; it is
mediated by bradykinin, a substance released from the lungs during initial inflation.

• Complete anatomical obliteration by proliferation of the intima is thought to take

1 to 3 months. In the adult, the obliterated ductus arteriosus forms the ligamentum
arteriosum.

Closure of the oval foramen is caused

• by an increased pressure in the left atrium, combined with
• a decrease in pressure on the right side.

• The first breath presses the septum primum against the septum secundum.

• During the first days of life, however, this closure is reversible. Crying by the
baby creates a shunt from right to left, which accounts for cyanotic periods in
the newborn.

• Constant apposition gradually leads to fusion of the two septa in about 1 year.
In 20% of individuals, however, perfect anatomical closure may never be
obtained (probe patent foramen ovale).