Which structure is not functioning in fetal circulation?

In fetal circulation, the lungs are not functioning as they do after birth. Instead of oxygenating blood, the fetus receives oxygenated blood through the placenta via the umbilical cord. This means that structures like the ductus arteriOSus and foramen ovale facilitate blood flow, bypassing the non-functioning lungs. After birth, these structures close, allowing normal pulmonary circulation to occur.