Fetus and newborn blood circulation

Because a mother's placenta does the work of exchanging oxygen (O2) and carbon dioxide (CO2) through the mother's circulation, a fetus' lungs are not used for breathing.

Instead of blood flowing to the lungs to pick up oxygen and then flowing to the rest of the body, the fetal circulation shunts (bypasses) most of the blood away from the lungs. In the fetus, blood is shunted from the pulmonary artery to the patent ductus arteriosus.

With the first breaths of air your baby takes at birth, the fetal circulation changes. A larger amount of blood is sent to the lungs to pick up oxygen.

• Because the patent ductus arteriosus is no longer needed, it begins to narrow and close off.
• The circulation in the lungs increases and more blood flows into the left atrium of the heart. This increased pressure causes the foramen ovale to close and blood circulates normally.