Maternity Nursing: Antepartum Q 40
Which of the following answers best describes the stage of pregnancy in which maternal and fetal blood are exchanged?
A. Conception
B. 9 weeks’ gestation, when the fetal heart is well developed.
C. 32-34 weeks gestation
D. Maternal and fetal blood are never exchanged.
Correct Answer: D. Maternal and fetal blood are never exchanged.
Only nutrients and waste products are transferred across the placenta. Blood exchange only occurs in complications and some medical procedures accidentally. The fetal circulation system is distinctly different from adult circulation. This intricate system allows the fetus to receive oxygenated blood and nutrients from the placenta. It comprises the blood vessels in the placenta and the umbilical cord, which contains two umbilical arteries and one umbilical vein.
Option A: The placenta connects the fetus to the wall of the uterus. It provides oxygen and nutrients from the mother to the growing fetus and also removes metabolic wastes and carbon dioxide from the fetus via the blood vessels in the umbilical cord. The umbilical cord develops from the placenta and is attached to the fetus.
Option B: Oxygenated blood from the mother in the placenta flows through the umbilical vein and into the inferior vena cava (IVC), bypassing the liver via the ductus venosus. From the IVC, oxygenated blood travels to the right atrium of the heart. There is greater pressure in the right atrium compared to the left atrium in fetal circulation; therefore most of the blood is shunted from the right atrium to the left atrium through an opening called the foramen ovale. Once in the left atrium, blood travels through the left ventricle into the aorta and the systemic circulation.
Option C: The deoxygenated blood travels back to the placenta via the umbilical arteries to be oxygenated by the mother. Additionally, some oxygenated blood in the right atrium can also enter the right ventricle and then the pulmonary artery. Because there is high resistance to blood flow in the lungs, the blood is shunted from the pulmonary artery into the aorta via the ductus arteriosus, hence bypassing the lungs. Blood then enters the systemic circulation, and the deoxygenated blood is recycled back to the mother via the umbilical arteries.