Congenital interruption of the alimentary canal, caused by abnormal development in its blood circulation, so serious in some cases that part of the canal is completely missing. The most frequent position of this abnormality is in the small intestine (1 in 4000 births). All such abnormalities can easily be diagnosed shortly after birth from the symptoms. In the case of atresia of the small intestine the baby spits out food, followed by yellowish-green vomit (bile); the abdomen dilates and meconium is not passed. Atresia of the oesophagus usually occurs in combination with a fistula between the lower part of the oesophagus and the windpipe, in consequence of which food often gets into the air passages, causes the child to become tight in the chest, blow bubbles, or breathe stertorously. Pneumonia can result from swallowing the wrong way. Atresia of the anus is easily recognized because there is no anal opening, just a retraction of the skin, and meconium is not passed. Symptoms of obstruction such as vomiting and a swollen abdomen occur somewhat later. Intestinal atresia may be suspected during pregnancy if there is a great deal of amniotic fluid, because it is not being absorbed by the baby. The absence of meconium for 24 hours after birth is also a sign but mucoviscidosis and meconium ileus are also possibilities. Treatment is usually possible by surgery.