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There is much natural variation in the growth of the fetus. Approximately 40% of the variation in birth weight can be accounted for by genetic factors, whereas 60% can be accounted for by environmental factors. Ultimately, the baby should be able to live up to its term growth potential. Factors affecting fetal growth can be maternal, placental, or fetal.
Maternal factors include maternal size, weight, weight for height , nutritional state , anemia, cigarette smoking, substance abuse, or uterine blood flow .
Placental factors include size, microstructure (densities and architecture), umbilical blood flow , transporters and binding proteins, nutrient utilization and nutrient production.
Fetal factors include the fetus genome, nutrient production, and hormone output.
Inappropriate growth can result in low birth weight. If the newborn is small for gestational age , he or she will have an increased risk for perinatal mortality ( deathThis page deals with death, the cessation of life. For other meanings of death, see death (disambiguation). Death is a term that can refer to either the termination of life in a living system, or the state of that organism after that event. A common perce shortly after birth), asphyxiaAsphyxia is a condition of severely deficient supply of oxygen to the body. In the absence of remedial action it will very rapidly lead to unconsciousness and death. Asphyxia is the same as suffocation and anoxia. Asphyxiation is the act of causing asphyx, hypothermiaHypothermia is a medical condition in which the victim's core body temperature has dropped to significantly below normal and normal metabolism begins to be impaired. This begins to occur when the core temperature drops below 35 degrees Celsius (95 degrees, polycythemiaPolycythemia is a condition in which there is a net increase in the total circulating erythrocyte (red blood cell) mass of the body. There are several types of polycythemia. Primary polycythemia ( vera ) Primary polycythemia often called polycythemia vera, hypocalcemia, immune dysfunction , neurologic abnormalities, and other long-term health problems. This can be the result of fetal growth restriction.
The circulatory systemThe circulatory system or cardiovascular system is the organ system which circulates blood around the body of most animals. Functions Following are some basic functions of the human circulatory system: #Delivery of oxygen and nutrients to all parts of the of a human fetus works differently from that of born humans, mainly because the lungs are not in use: the fetus obtains oxygenOxygen is the chemical element in the periodic table that has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe. Molecular oxygen (O, often called free oxygen on Earth is thermodynamically un and nutrients from the mother through the placenta and the umbilical cord.
Blood from the placenta is carried by the umbilical vein. About half of this enters the 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, then 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 placental arteries, and re-enters the placenta, where carbon dioxide and other waste products from the fetus are taken up and enter the mother's circulation.
Some of the blood from the right atrium does not enter the left atrium, but enters the right ventricle and is pumped into the pulmonary artery. In the fetus, there is a special connection between the pulmonary artery and the aorta, called the ductus arteriosus, which directs most of this blood away from the lungs (which aren't being used for respiration at this point as the fetus is suspended in amniotic fluid).
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