Smoking during pregnancy may affect the development of the fetus or even lead to death, cause defects or malformations in the newborn, and affect the intellectual development of the fetus. 1. Affecting fetal development or even leading to death: when smoking during pregnancy, nicotine and carbon monoxide from cigarettes will enter the bloodstream, leading to fetal hypoxia, affecting fetal development or even leading to stillbirth. 2. Newborn defects and malformations: smoking during pregnancy causes fetal underdevelopment, and the probability of being born with defects or even malformations will be greatly increased, so smoking during pregnancy should be avoided. 3. Impact on fetal intelligence: Harmful substances in cigarettes may lead to a decrease in vitamin B12 content in the body, which will have an adverse effect on fetal neurodevelopment and lead to a decrease in the intelligence of newborns. Therefore, pregnant women should quit smoking and avoid inhaling second-hand smoke.