5. Heart and circulation in the unborn baby

       The main difference in the circulation of an unborn baby is the fact that the lungs have no function within the mother's womb. The baby is floating in fluid and the lungs are therefore in a collapsed state. The baby gets oxygen rich blood from the mother's circulation through the placenta. This blood passes from the right upper chamber into the left side of the heart through a hole in the atrial septum (wall between the two top chambers of the heart) which is called the patent foramen ovale (PFO). This hole usually seals off after birth but in 30% of people can still remain open in adult life. This is a normal finding and should not cause any alarm.
       The oxygen rich blood that has reached the left side of the heart is then circulated through the body via the aorta to supply the brain and other organs of the baby. The right side of the heart contains oxygen poor blood and this is pumped into the pulmonary artery (artery to the lung). As the lungs are collapsed this blood does not really have an easy way forward and is diverted through the ductus arteriosus or 'duct' into the aorta which supplies the lower half of the body.

       This form of circulation ensures that important organs like the brain get oxygen rich blood whilst the peripheral organs make do with oxygen poor blood. The duct usually closes within a few days after birth. In some babies particularly premature babies the duct can remain open leading to Persistent Ductus Arteriosus or PDA which may need closure in later life.