Smoking by men can have adverse effects on the fetus. Smoke from burning tobacco contains nicotine, tar and carbon monoxide, which can cross the placental barrier and affect the normal development of the fetus. Carbon monoxide affects the fetus’s access to oxygen. A man who smokes for a long period of time next to a pregnant woman will cause the fetus to suffer from a lack of oxygen, which will affect the fetus’s physical development, especially its mental development. If a man smokes beside a pregnant woman for a long time, and the pregnant woman is exposed to second-hand smoke, the fetus is at risk of malnutrition, and the probability of intrauterine fetal death is also very high. Frequent passive smoking by pregnant women can lead to malformations in the development of the fetus’s face or mouth, which can lead to many dental problems. Smoking by men can lead to excessive intake of toxins by pregnant women, which may result in congenital malformations of the fetus, with loss of limbs, fingers, organs and other parts of the body, and the fetus will be born lighter compared to other newborns, which will have a significant difference in terms of weight. A large amount of nicotine will cause great harm to human respiration, especially for the development of the respiratory system of the fetus has a great impact, some fetuses can be born with bronchitis, pneumonia, asthma and other respiratory diseases.