<Tr> <Td_colspan="2"> Anatomical terminology (edit on Wikidata) </Td> </Tr> <P> In animals that give live birth, the fetal circulation is the circulatory system of a fetus . The term usually encompasses the entire fetoplacental circulation, which includes the umbilical cord and the blood vessels within the placenta that carry fetal blood . </P> <P> The fetal (prenatal) circulation works differently from normal postnatal circulation, mainly because the lungs are not in use . Instead, the fetus obtains oxygen and nutrients from the mother through the placenta and the umbilical cord . The advent of breathing and the severance of the umbilical cord prompt various neuroendocrine changes that shortly transform fetal circulation into postnatal circulation . </P> <P> The fetal circulation of humans has been extensively studied by the health sciences . Much is known also of fetal circulation in other animals, especially livestock and model organisms such as mice, through the health sciences, veterinary science, and life sciences generally . </P>

When is the cardiovascular system functioning in a fetus