<P> Fetal pain, its existence and its implications are debated politically and academically . According to the conclusions of a review published in 2005, "Evidence regarding the capacity for fetal pain is limited but indicates that fetal perception of pain is unlikely before the third trimester ." However, developmental neurobiologists argue that the establishment of thalamocortical connections (at about 6 - 1 / 2 months) is an essential event with regard to fetal perception of pain . Nevertheless, the perception of pain involves sensory, emotional and cognitive factors and it is "impossible to know" when pain is experienced, even if it is known when thalamocortical connections are established . Some authors argue that fetal pain is possible from the second half of pregnancy: "The available scientific evidence makes it possible, even probable, that fetal pain perception occurs well before late gestation" wrote KJS Anand in the journal of the IASP . </P> <P> Whether a fetus has the ability to feel pain and suffering is part of the abortion debate . In the United States, for example, pro-life advocates have proposed legislation that would require providers of abortions to inform women that their fetuses may feel pain during the procedure and that would require each woman to accept or decline anesthesia for the fetus . </P> <P> The heart and blood vessels which form the circulatory system, form relatively early during embryonic development, but continue to grow and develop in complexity in the growing fetus . A functional circulatory system is a biological necessity, since mammalian tissues cannot grow more than a few cell layers thick without an active blood supply . The prenatal circulation of blood is different than the postnatal circulation, mainly because the lungs are not in use . The fetus obtains oxygen and nutrients from the mother through the placenta and the umbilical cord . </P> <P> Blood from the placenta is carried to the fetus by the umbilical vein . About half of this enters the fetal ductus venosus and is carried to the inferior vena cava, while the other half enters the liver proper from the inferior border of the liver . The branch of the umbilical vein that supplies the right lobe of the liver first joins with the portal vein . The blood then moves to the right atrium of the heart . In the fetus, there is an opening between the right and left atrium (the foramen ovale), and most of the blood flows from the right into the left atrium, thus bypassing pulmonary circulation . The majority of blood flow is into the left ventricle from where it is pumped through the aorta into the body . Some of the blood moves from the aorta through the internal iliac arteries to the umbilical arteries, and re-enters the placenta, where carbon dioxide and other waste products from the fetus are taken up and enter the woman's circulation . </P>

When do the organs develop in a fetus