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There is much natural variation in the growth of the fetus. 40% of the variation in birth weight is due to genetic factors, whereas 60% is due to 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.
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, asphyxia, hypothermia, polycythemia, hypocalcemia, immune dysfunction, neurologic abnormalities, and other long-term health sequelae. This can be the result of fetal growth restriction.
Compare the design of the adult and fetal circulations. Describe the organization of series and parallel circuits for blood flow ==
- Right and left ventricles pump in parallel
- oxygen saturation of blood in the umbilical vein is high, though only 80% saturated as compared with 98% in pulmonary veins
- arterial blood has 60% oxygen saturation, compared with 98% in adult arterial blood
What is the significance of the high blood flow to the placenta in the fetus?
- Placenta is a huge shunt in fetal circulation
- high flow results from low vascular resistance
- high flow necessary for appropriate exchange of substances with maternal circulation
Identify "shunts" in the fetal circulation and describe their functional significance
- ductus venosus (DV) - umbilical vein joins portal flow in the liver and is shunted in part into the inferior vena cava by the DV
- foramen ovale (FO) - blood returning into right atrium is shunted into the left atrium
- ductus arteriosus - shunt between the pulmonary artery and the aorta