In the late stages of pregnancy, whether diarrhea caused by dietary carelessness affects the fetus mainly depends on the severity of the condition. First, if it's just mild diarrhea without causing severe abdominal pain or significant dehydration, it generally doesn't affect the fetus. This type of diarrhea can be managed through dietary adjustments. Second, if the diarrhea is very severe in late pregnancy, causing noticeable abdominal pain, difficulty eating, or dehydration, it may lead to uterine contractions and maternal malnutrition. This could potentially impact fetal development or cause premature birth. In such cases, early medical intervention is necessary. Oral Smecta can be used for treatment, and if needed, stool analysis and blood chemistry tests should be performed. Intravenous fluids may be required to prevent further complications.