There are many causes of bad breath in pregnant women, such as changes in estrogen levels, oral diseases, gastrointestinal disorders and so on. Changes in estrogen levels: During pregnancy, estrogen levels rise in the body, coupled with the different physical qualities of individuals, most of them will have different degrees of taste and appetite changes, especially with nausea and vomiting as a common phenomenon. Therefore, it may lead to the phenomenon of bad breath in pregnant women. 2. Oral disease: Halitosis in pregnant women may also be due to their own gingivitis, dental caries, periodontitis and other oral diseases. 3. Gastrointestinal diseases: pregnant women with improper diet, irregular diet, early pregnancy reaction and other factors, may lead to gastrointestinal dysfunction, indigestion and other conditions, which may cause bad breath in pregnant women. There are many causes of halitosis in pregnant women, if the symptoms appear for a long time, it is recommended that pregnant women go to the hospital in time to improve the examination and give standardized treatment after a clear diagnosis.