Why Do Some Babies Have Congenital Heart Defects?
The human heart begins to form as a single tubular structure at about the fourth week of pregnancy. By the eighth week, this tube will gradually increase in length, eventually twisting upon itself. A wall, or septum, grows to divide the upper (atrial) and lower (ventricular) chambers into left and right sides. Four valves made of tissue develop, which will keep blood moving forward through the cardiac chambers, lungs, and body as the heart pumps. Because the placenta (and not the fetus’ lungs) does the work of exchanging oxygen and carbon dioxide, it’s possible for even severe developmental abnormalities of the heart to exist without causing difficulties for the fetus. Such abnormalities may become important only after the fetus’ circulation transitions to the newborn state after birth (when the umbilical cord is clamped at the time of delivery, the placenta is no longer involved in the baby’s circulation). The newborn becomes dependent upon the lungs and circulatory system for the oxy
