Black stool in pregnancy is divided into two major causes: physiological and pathological. The former is mainly related to diet or medication, while the latter may be caused by gastrointestinal bleeding, etc. You should go to the obstetrics department for an examination and let the doctor determine the cause. 1. Physiological causes: black stools can be caused by intake of iron or nutritional supplements containing iron during pregnancy, and excessive intake of iron-containing foods, such as animal liver and pig’s blood, etc. This is due to the fact that iron interacts with iron in the intestines. This is due to the combination of iron and hydrogen sulfide in the intestines to generate iron sulfide, which is the main cause of black stools during pregnancy. Physiologic black stools have no other discomfort, and the symptoms can disappear after stopping the intake of iron. 2. Pathological reasons: If pregnant women suffer from digestive diseases, such as acute and chronic gastritis, peptic ulcer, etc., due to the damage of the digestive tract mucosa, may lead to upper gastrointestinal bleeding, when the blood enters the intestine, under the action of bacteria to make the iron in hemoglobin into iron sulfide, so the stool can also become black. Pregnant women usually may have other symptoms, such as abdominal pain, acid reflux, etc.. Pregnant women with black stools should first exclude physiological factors, if they are taking iron supplements, and there are no other accompanying symptoms can be observed for the time being; do not eat iron-containing medicines or foods, and at the same time there are epigastric discomfort and other manifestations should be promptly consulted for examination, and under the guidance of the doctor reasonable treatment.