A small amount of drinking and smoking before pregnancy will have a relatively small effect on the fetus. A large amount of long-term smoking and drinking before pregnancy may affect the fetus and make it easy to have a miscarriage, fetal developmental deformities, intellectual disabilities, etc. during pregnancy, but not absolutely.
A small amount of smoking and drinking by both men and women before pregnancy may have a smaller effect on the quality of eggs and sperm, which will have a smaller effect on the fetus, but the specific situation varies from person to person.
If both men and women or a single party smoke and drink a lot for a long time before pregnancy, the tar in cigarettes and the ethanol in alcohol are toxic to the human brain, liver and heart, and enter the fetus through the placenta, which may affect the development of the fetus and so on.
Although these effects are not absolute, but for the sake of eugenics, it is recommended to avoid contact with alcohol and tobacco during preparation and pregnancy. If you are pregnant, you should continue the pregnancy with a proper maternity checkup and terminate the pregnancy promptly if you find any serious abnormalities.