The fetus breathes through the placenta. When the function of the placenta declines, it can lead to fetal hypoxia, which requires prompt medical treatment. Fetal lungs are not yet well developed in the mother’s body, the alveoli lack lung surface active substances, and the alveoli are not tense, so they can’t carry out respiratory movements normally to complete gas exchange. However, the oxygen in the mother’s body can pass through the placenta through simple diffusion and enter into the body of the fetus, and the carbon dioxide in the body of the fetus can be metabolized out of the fetus’s body through the placenta, so the fetus’ respiration is completed by the placenta. When the function of the placenta declines can lead to fetal hypoxia, resulting in intrauterine distress, which requires prompt medical attention and treatment to avoid fetal death in the womb, leading to an adverse pregnancy outcome.