With OA, the oesophagus does not connect the mouth and stomach properly, but forms a closed off pouch that prevents food from reaching the stomach. If it is not corrected, this pouch can fill up with food and saliva, which can eventually overflow into the baby's trachea (windpipe), entering the lungs and causing choking. With TOF, usually the lower part of the oesophagus is connected to the windpipe. Without treatment, this causes air to pass from the windpipe to the food pipe and stomach. It can also allow stomach acid to pass into the lungs.
Most commonly, babies have both TOF and OA, though on rare occasions either TOF or OA can occur on their own.
Babies with TOF/OA may also have other health problems, particularly heart defects, imperforate anus (opening to the anus is missing or blocked) and problems with the kidneys, spine and limbs. There is a recognised association between a particular group of difficulties, which has been called the VACTERL Association.