Occasional exposure to secondhand smoke in early pregnancy will have no effect on the fetus. Prolonged exposure to secondhand smoke may increase the chances of abnormal development of the fetus and may also affect its normal growth. Early pregnancy is only occasional second-hand smoke, usually do not have contact with, will not cause any effect on the fetus. Secondhand smoke contains a large number of toxic substances, such as nicotine, hydrocyanic acid, ammonia, carbon monoxide, carbon dioxide, pyridine, aromatic compounds, tar and so on, and prolonged exposure in early pregnancy will have an impact on the fetus. These harmful substances will be absorbed into the mother’s bloodstream along with the smoke, and then affect the fetus through the placenta. Early pregnancy is an important period for the formation of embryonic differentiation, which may increase the chances of abnormal development of the fetus, such as anencephaly, cleft palate, cleft lip, dementia, and increase the occurrence of congenital heart disease. Prolonged exposure to secondhand smoke in early pregnancy may cause growth retardation of the fetus, resulting in its low birth weight and weaker body after birth. Therefore, women should stay away from secondhand smoke during pregnancy, try to stay in a fresh air environment, and if they have any symptoms of physical discomfort, they should go to the hospital and consult a physician for guidance.