Final answer:
During pregnancy, the respiratory minute volume increases by about 50% to support the fetus, but can cause shortness of breath as the uterus expands. Around week 28, the fetus has developed enough to breathe on its own, and the mother undergoes significant circulatory changes, including an increased blood volume by 30%.
Step-by-step explanation:
Changes in Pulmonary Function During Pregnancy
During pregnancy, the respiratory system undergoes significant changes to support the developing fetus. Around the second half of pregnancy, the respiratory minute volume, which is the volume of gas inhaled or exhaled by the lungs per minute, increases by about 50 percent. This is an adaptation to meet the increased oxygen requirements of the fetus and the mother's elevated metabolic rate. However, the expanding uterus puts pressure on the diaphragm, which can reduce the volume of each breath and lead to dyspnea, or shortness of breath. As pregnancy progresses to the final weeks, the pelvis becomes more elastic, allowing the fetus to descend lower in a process known as lightening, often providing some relief from dyspnea.
Concurrently, during gestation, notable respiratory system developments occur in the fetus from week 24 until term. This period sees an increase in the number of alveolar precursors and the production of pulmonary surfactant, which is crucial for lung compliance and breathing at birth. Typically, enough alveolar maturation is present by week 28 for a prematurely born baby to breathe independently, though full maturation continues into childhood. Moreover, maternal physiological adaptations include a 30 percent increase in blood volume and changes in the circulatory system to support fetal nourishment and waste removal.